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 $92.90   11.120%   $103.2305   $103.23   $103.25   $103.20  
  Purchase #2 $189.41   9.272%   $206.9721   $206.97   $206.95   $207.00  
  Purchase #3 $96.66   6.501%   $102.9439   $102.94   $102.95   $102.90  
  Purchase #4 $136.90   12.518%   $154.0371   $154.04   $154.05   $154.00  
  Purchase #5 $119.96   7.625%   $129.107   $129.11   $129.10   $129.10  
  Purchase #6 $165.85   6.721%   $176.9968   $177.00   $177.00   $177.00  
  Purchase #7 $91.93   5.479%   $96.9668   $96.97   $96.95   $97.00  
  7 purchase totals = $893.61       $970.2542   $970.26   $970.25   $970.20