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 $82.67   7.201%   $88.6231   $88.62   $88.60   $88.60  
  Purchase #2 $12.39   12.692%   $13.9625   $13.96   $13.95   $14.00  
  Purchase #3 $234.96   9.855%   $258.1153   $258.12   $258.10   $258.10  
  Purchase #4 $73.34   10.665%   $81.1617   $81.16   $81.15   $81.20  
  Purchase #5 $77.45   9.631%   $84.9092   $84.91   $84.90   $84.90  
  Purchase #6 $41.69   7.707%   $44.903   $44.90   $44.90   $44.90  
  Purchase #7 $241.84   5.155%   $254.3069   $254.31   $254.30   $254.30  
  7 purchase totals = $764.34       $825.9817   $825.98   $825.90   $826.00