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 $249.47   11.147%   $277.2784   $277.28   $277.30   $277.30  
  Purchase #2 $68.65   9.311%   $75.042   $75.04   $75.05   $75.00  
  Purchase #3 $150.52   9.800%   $165.271   $165.27   $165.25   $165.30  
  Purchase #4 $33.78   8.727%   $36.728   $36.73   $36.75   $36.70  
  Purchase #5 $121.30   8.635%   $131.7743   $131.77   $131.75   $131.80  
  Purchase #6 $104.80   10.189%   $115.4781   $115.48   $115.50   $115.50  
  Purchase #7 $67.92   5.422%   $71.6026   $71.60   $71.60   $71.60  
  7 purchase totals = $796.44       $873.1744   $873.17   $873.20   $873.20