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 $177.73   13.852%   $202.3492   $202.35   $202.35   $202.30  
  Purchase #2 $97.48   5.260%   $102.6074   $102.61   $102.60   $102.60  
  Purchase #3 $145.62   9.562%   $159.5442   $159.54   $159.55   $159.50  
  Purchase #4 $91.62   4.495%   $95.7383   $95.74   $95.75   $95.70  
  Purchase #5 $123.67   8.486%   $134.1646   $134.16   $134.15   $134.20  
  Purchase #6 $109.59   9.507%   $120.0087   $120.01   $120.00   $120.00  
  Purchase #7 $184.86   13.456%   $209.7348   $209.73   $209.75   $209.70  
  7 purchase totals = $930.57       $1,024.1472   $1,024.14   $1,024.15   $1,024.00