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 $43.66   13.732%   $49.6554   $49.66   $49.65   $49.70  
  Purchase #2 $126.33   5.421%   $133.1783   $133.18   $133.20   $133.20  
  Purchase #3 $56.82   9.132%   $62.0088   $62.01   $62.00   $62.00  
  Purchase #4 $23.37   12.773%   $26.3551   $26.36   $26.35   $26.40  
  Purchase #5 $169.37   10.830%   $187.7128   $187.71   $187.70   $187.70  
  Purchase #6 $82.74   3.761%   $85.8519   $85.85   $85.85   $85.90  
  Purchase #7 $97.47   10.303%   $107.5123   $107.51   $107.50   $107.50  
  7 purchase totals = $599.76       $652.2746   $652.28   $652.25   $652.40