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 $54.96   6.679%   $58.6308   $58.63   $58.65   $58.60  
  Purchase #2 $25.93   10.423%   $28.6327   $28.63   $28.65   $28.60  
  Purchase #3 $210.40   3.359%   $217.4673   $217.47   $217.45   $217.50  
  Purchase #4 $135.27   4.332%   $141.1299   $141.13   $141.15   $141.10  
  Purchase #5 $65.53   6.576%   $69.8393   $69.84   $69.85   $69.80  
  Purchase #6 $148.52   13.802%   $169.0187   $169.02   $169.00   $169.00  
  Purchase #7 $80.41   10.713%   $89.0243   $89.02   $89.00   $89.00  
  7 purchase totals = $721.02       $773.7430   $773.74   $773.75   $773.60