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 $247.54   6.515%   $263.6672   $263.67   $263.65   $263.70  
  Purchase #2 $60.49   10.356%   $66.7543   $66.75   $66.75   $66.80  
  Purchase #3 $51.32   6.280%   $54.5429   $54.54   $54.55   $54.50  
  Purchase #4 $78.34   11.465%   $87.3217   $87.32   $87.30   $87.30  
  Purchase #5 $86.82   5.479%   $91.5769   $91.58   $91.60   $91.60  
  Purchase #6 $80.29   4.872%   $84.2017   $84.20   $84.20   $84.20  
  Purchase #7 $94.46   8.353%   $102.3502   $102.35   $102.35   $102.40  
  7 purchase totals = $699.26       $750.4149   $750.41   $750.40   $750.50