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 $193.51   10.379%   $213.5944   $213.59   $213.60   $213.60  
  Purchase #2 $195.25   11.116%   $216.954   $216.95   $216.95   $217.00  
  Purchase #3 $206.31   6.826%   $220.3927   $220.39   $220.40   $220.40  
  Purchase #4 $96.67   8.199%   $104.596   $104.60   $104.60   $104.60  
  Purchase #5 $134.99   11.284%   $150.2223   $150.22   $150.20   $150.20  
  Purchase #6 $87.60   6.283%   $93.1039   $93.10   $93.10   $93.10  
  Purchase #7 $243.78   10.207%   $268.6626   $268.66   $268.65   $268.70  
  7 purchase totals = $1,158.11       $1,267.5259   $1,267.51   $1,267.50   $1,267.60