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 $172.78   12.732%   $194.7783   $194.78   $194.80   $194.80  
  Purchase #2 $108.67   6.455%   $115.6846   $115.68   $115.70   $115.70  
  Purchase #3 $199.25   3.374%   $205.9727   $205.97   $205.95   $206.00  
  Purchase #4 $5.80   5.374%   $6.1117   $6.11   $6.10   $6.10  
  Purchase #5 $41.27   11.622%   $46.0664   $46.07   $46.05   $46.10  
  Purchase #6 $236.98   4.543%   $247.746   $247.75   $247.75   $247.70  
  Purchase #7 $156.63   6.663%   $167.0663   $167.07   $167.05   $167.10  
  7 purchase totals = $921.38       $983.4260   $983.43   $983.40   $983.50