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 $127.94   13.475%   $145.1799   $145.18   $145.20   $145.20  
  Purchase #2 $210.74   13.293%   $238.7537   $238.75   $238.75   $238.80  
  Purchase #3 $119.84   10.638%   $132.5886   $132.59   $132.60   $132.60  
  Purchase #4 $209.68   11.108%   $232.9713   $232.97   $232.95   $233.00  
  Purchase #5 $84.79   13.412%   $96.162   $96.16   $96.15   $96.20  
  Purchase #6 $39.56   5.517%   $41.7425   $41.74   $41.75   $41.70  
  Purchase #7 $54.58   8.264%   $59.0905   $59.09   $59.10   $59.10  
  7 purchase totals = $847.13       $946.4885   $946.48   $946.50   $946.60