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 $213.40   11.405%   $237.7383   $237.74   $237.75   $237.70  
  Purchase #2 $12.34   3.236%   $12.7393   $12.74   $12.75   $12.70  
  Purchase #3 $100.39   6.138%   $106.5519   $106.55   $106.55   $106.60  
  Purchase #4 $226.41   12.192%   $254.0139   $254.01   $254.00   $254.00  
  Purchase #5 $128.75   8.238%   $139.3564   $139.36   $139.35   $139.40  
  Purchase #6 $74.33   7.700%   $80.0534   $80.05   $80.05   $80.10  
  Purchase #7 $165.29   11.208%   $183.8157   $183.82   $183.80   $183.80  
  7 purchase totals = $920.91       $1,014.2689   $1,014.27   $1,014.25   $1,014.30