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 $51.54   13.696%   $58.5989   $58.60   $58.60   $58.60  
  Purchase #2 $48.35   3.341%   $49.9654   $49.97   $49.95   $50.00  
  Purchase #3 $152.91   4.332%   $159.5341   $159.53   $159.55   $159.50  
  Purchase #4 $192.98   7.270%   $207.0096   $207.01   $207.00   $207.00  
  Purchase #5 $189.97   5.557%   $200.5266   $200.53   $200.55   $200.50  
  Purchase #6 $131.48   12.108%   $147.3996   $147.40   $147.40   $147.40  
  Purchase #7 $92.55   10.394%   $102.1696   $102.17   $102.15   $102.20  
  7 purchase totals = $859.78       $925.2038   $925.21   $925.20   $925.20