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 $215.34   12.218%   $241.6502   $241.65   $241.65   $241.70  
  Purchase #2 $242.79   10.321%   $267.8484   $267.85   $267.85   $267.80  
  Purchase #3 $211.69   4.651%   $221.5357   $221.54   $221.55   $221.50  
  Purchase #4 $106.82   9.634%   $117.111   $117.11   $117.10   $117.10  
  Purchase #5 $217.33   4.108%   $226.2579   $226.26   $226.25   $226.30  
  Purchase #6 $201.97   9.630%   $221.4197   $221.42   $221.40   $221.40  
  Purchase #7 $93.96   5.403%   $99.0367   $99.04   $99.05   $99.00  
  7 purchase totals = $1,289.90       $1,394.8596   $1,394.87   $1,394.85   $1,394.80