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 $113.65   11.722%   $126.9721   $126.97   $126.95   $127.00  
  Purchase #2 $13.71   8.790%   $14.9151   $14.92   $14.90   $14.90  
  Purchase #3 $64.80   11.656%   $72.3531   $72.35   $72.35   $72.40  
  Purchase #4 $26.62   5.603%   $28.1115   $28.11   $28.10   $28.10  
  Purchase #5 $178.87   8.830%   $194.6642   $194.66   $194.65   $194.70  
  Purchase #6 $212.73   5.419%   $224.2578   $224.26   $224.25   $224.30  
  Purchase #7 $212.65   5.220%   $223.7503   $223.75   $223.75   $223.80  
  7 purchase totals = $823.03       $885.0241   $885.02   $884.95   $885.20