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 $66.87   5.806%   $70.7525   $70.75   $70.75   $70.80  
  Purchase #2 $48.38   13.447%   $54.8857   $54.89   $54.90   $54.90  
  Purchase #3 $203.65   10.184%   $224.3897   $224.39   $224.40   $224.40  
  Purchase #4 $110.49   6.424%   $117.5879   $117.59   $117.60   $117.60  
  Purchase #5 $35.37   4.357%   $36.9111   $36.91   $36.90   $36.90  
  Purchase #6 $218.72   5.711%   $231.2111   $231.21   $231.20   $231.20  
  Purchase #7 $31.86   5.532%   $33.6225   $33.62   $33.60   $33.60  
  7 purchase totals = $715.34       $769.3605   $769.36   $769.35   $769.40