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 $85.93   7.391%   $92.2811   $92.28   $92.30   $92.30  
  Purchase #2 $22.39   8.463%   $24.2849   $24.28   $24.30   $24.30  
  Purchase #3 $191.49   5.726%   $202.4547   $202.45   $202.45   $202.50  
  Purchase #4 $42.86   5.124%   $45.0561   $45.06   $45.05   $45.10  
  Purchase #5 $139.85   11.568%   $156.0278   $156.03   $156.05   $156.00  
  Purchase #6 $68.58   4.764%   $71.8472   $71.85   $71.85   $71.80  
  Purchase #7 $200.96   5.625%   $212.264   $212.26   $212.25   $212.30  
  7 purchase totals = $752.06       $804.2158   $804.21   $804.25   $804.30