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 $57.61   3.872%   $59.8407   $59.84   $59.85   $59.80  
  Purchase #2 $113.31   10.399%   $125.0931   $125.09   $125.10   $125.10  
  Purchase #3 $185.47   9.263%   $202.6501   $202.65   $202.65   $202.70  
  Purchase #4 $167.26   7.136%   $179.1957   $179.20   $179.20   $179.20  
  Purchase #5 $46.81   6.311%   $49.7642   $49.76   $49.75   $49.80  
  Purchase #6 $78.44   8.113%   $84.8038   $84.80   $84.80   $84.80  
  Purchase #7 $92.75   7.822%   $100.0049   $100.00   $100.00   $100.00  
  7 purchase totals = $741.65       $801.3525   $801.34   $801.35   $801.40