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 $167.59   3.231%   $173.0048   $173.00   $173.00   $173.00  
  Purchase #2 $182.47   11.821%   $204.0398   $204.04   $204.05   $204.00  
  Purchase #3 $24.61   7.777%   $26.5239   $26.52   $26.50   $26.50  
  Purchase #4 $204.96   11.854%   $229.256   $229.26   $229.25   $229.30  
  Purchase #5 $182.55   6.702%   $194.7845   $194.78   $194.80   $194.80  
  Purchase #6 $66.74   13.796%   $75.9475   $75.95   $75.95   $75.90  
  Purchase #7 $126.99   12.801%   $143.246   $143.25   $143.25   $143.20  
  7 purchase totals = $955.91       $1,046.8025   $1,046.80   $1,046.80   $1,046.70