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 $62.34   10.136%   $68.6588   $68.66   $68.65   $68.70  
  Purchase #2 $235.41   3.296%   $243.1691   $243.17   $243.15   $243.20  
  Purchase #3 $178.70   6.351%   $190.0492   $190.05   $190.05   $190.00  
  Purchase #4 $93.33   11.537%   $104.0975   $104.10   $104.10   $104.10  
  Purchase #5 $57.47   10.103%   $63.2762   $63.28   $63.30   $63.30  
  Purchase #6 $183.33   9.824%   $201.3403   $201.34   $201.35   $201.30  
  Purchase #7 $139.44   7.129%   $149.3807   $149.38   $149.40   $149.40  
  7 purchase totals = $950.02       $1,019.9718   $1,019.98   $1,020.00   $1,020.00