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   4.249%   $64.9888   $64.99   $65.00   $65.00  
  Purchase #2 $144.64   5.818%   $153.0552   $153.06   $153.05   $153.10  
  Purchase #3 $173.77   13.670%   $197.5244   $197.52   $197.50   $197.50  
  Purchase #4 $56.50   11.554%   $63.028   $63.03   $63.05   $63.00  
  Purchase #5 $101.68   13.245%   $115.1475   $115.15   $115.15   $115.10  
  Purchase #6 $156.49   8.570%   $169.9012   $169.90   $169.90   $169.90  
  Purchase #7 $28.34   12.409%   $31.8567   $31.86   $31.85   $31.90  
  7 purchase totals = $723.76       $795.5018   $795.51   $795.50   $795.50