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 $58.46   11.541%   $65.2069   $65.21   $65.20   $65.20  
  Purchase #2 $202.64   6.736%   $216.2898   $216.29   $216.30   $216.30  
  Purchase #3 $69.85   13.142%   $79.0297   $79.03   $79.05   $79.00  
  Purchase #4 $113.86   10.239%   $125.5181   $125.52   $125.50   $125.50  
  Purchase #5 $152.69   9.575%   $167.3101   $167.31   $167.30   $167.30  
  Purchase #6 $44.73   11.355%   $49.8091   $49.81   $49.80   $49.80  
  Purchase #7 $172.62   3.456%   $178.5857   $178.59   $178.60   $178.60  
  7 purchase totals = $814.85       $881.7494   $881.76   $881.75   $881.70