Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $96.30   8.755%   $104.7311   $104.73   $104.75   $104.70  
  Purchase #2 $111.37   13.803%   $126.7424   $126.74   $126.75   $126.70  
  Purchase #3 $212.89   6.367%   $226.4447   $226.44   $226.45   $226.40  
  Purchase #4 $241.99   11.699%   $270.3004   $270.30   $270.30   $270.30  
  Purchase #5 $217.27   7.817%   $234.254   $234.25   $234.25   $234.30  
  Purchase #6 $162.64   12.530%   $183.0188   $183.02   $183.00   $183.00  
  Purchase #7 $176.29   12.322%   $198.0125   $198.01   $198.00   $198.00  
  7 purchase totals = $1,218.75       $1,343.5039   $1,343.49   $1,343.50   $1,343.40