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 $59.48   6.398%   $63.2855   $63.29   $63.30   $63.30  
  Purchase #2 $120.26   7.230%   $128.9548   $128.95   $128.95   $129.00  
  Purchase #3 $180.78   12.233%   $202.8948   $202.89   $202.90   $202.90  
  Purchase #4 $239.32   9.830%   $262.8452   $262.85   $262.85   $262.80  
  Purchase #5 $15.98   3.324%   $16.5112   $16.51   $16.50   $16.50  
  Purchase #6 $183.75   10.611%   $203.2477   $203.25   $203.25   $203.20  
  Purchase #7 $202.86   13.700%   $230.6518   $230.65   $230.65   $230.70  
  7 purchase totals = $1,002.43       $1,108.3910   $1,108.39   $1,108.40   $1,108.40