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 $68.73   10.853%   $76.1893   $76.19   $76.20   $76.20  
  Purchase #2 $149.46   7.352%   $160.4483   $160.45   $160.45   $160.40  
  Purchase #3 $23.27   11.618%   $25.9735   $25.97   $25.95   $26.00  
  Purchase #4 $155.66   10.759%   $172.4075   $172.41   $172.40   $172.40  
  Purchase #5 $11.51   9.760%   $12.6334   $12.63   $12.65   $12.60  
  Purchase #6 $173.70   9.300%   $189.8541   $189.85   $189.85   $189.90  
  Purchase #7 $58.61   9.517%   $64.1879   $64.19   $64.20   $64.20  
  7 purchase totals = $640.94       $701.6940   $701.69   $701.70   $701.70