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 $118.96   4.129%   $123.8719   $123.87   $123.85   $123.90  
  Purchase #2 $55.59   6.414%   $59.1555   $59.16   $59.15   $59.20  
  Purchase #3 $181.28   4.251%   $188.9862   $188.99   $189.00   $189.00  
  Purchase #4 $90.90   11.352%   $101.219   $101.22   $101.20   $101.20  
  Purchase #5 $93.99   12.655%   $105.8844   $105.88   $105.90   $105.90  
  Purchase #6 $69.34   8.571%   $75.2831   $75.28   $75.30   $75.30  
  Purchase #7 $194.60   3.311%   $201.0432   $201.04   $201.05   $201.00  
  7 purchase totals = $804.66       $855.4433   $855.44   $855.45   $855.50