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 $50.32   13.759%   $57.2435   $57.24   $57.25   $57.20  
  Purchase #2 $144.28   5.818%   $152.6742   $152.67   $152.65   $152.70  
  Purchase #3 $138.84   7.865%   $149.7598   $149.76   $149.75   $149.80  
  Purchase #4 $46.29   13.324%   $52.4577   $52.46   $52.45   $52.50  
  Purchase #5 $212.74   5.713%   $224.8938   $224.89   $224.90   $224.90  
  Purchase #6 $44.98   13.404%   $51.0091   $51.01   $51.00   $51.00  
  Purchase #7 $63.95   7.326%   $68.635   $68.64   $68.65   $68.60  
  7 purchase totals = $701.40       $756.6731   $756.67   $756.65   $756.70