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 $104.34   5.734%   $110.3229   $110.32   $110.30   $110.30  
  Purchase #2 $218.93   8.387%   $237.2917   $237.29   $237.30   $237.30  
  Purchase #3 $107.78   12.609%   $121.37   $121.37   $121.35   $121.40  
  Purchase #4 $197.86   4.253%   $206.275   $206.28   $206.30   $206.30  
  Purchase #5 $125.70   13.422%   $142.5715   $142.57   $142.55   $142.60  
  Purchase #6 $91.83   11.713%   $102.586   $102.59   $102.60   $102.60  
  Purchase #7 $37.26   10.258%   $41.0821   $41.08   $41.10   $41.10  
  7 purchase totals = $883.70       $961.4992   $961.50   $961.50   $961.60