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 $34.99   5.657%   $36.9694   $36.97   $36.95   $37.00  
  Purchase #2 $56.57   8.232%   $61.2268   $61.23   $61.25   $61.20  
  Purchase #3 $99.47   6.745%   $106.1793   $106.18   $106.20   $106.20  
  Purchase #4 $112.59   9.425%   $123.2016   $123.20   $123.20   $123.20  
  Purchase #5 $68.66   7.207%   $73.6083   $73.61   $73.60   $73.60  
  Purchase #6 $202.53   10.756%   $224.3141   $224.31   $224.30   $224.30  
  Purchase #7 $45.52   5.825%   $48.1715   $48.17   $48.15   $48.20  
  7 purchase totals = $620.33       $673.6710   $673.67   $673.65   $673.70