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 $202.45   6.325%   $215.255   $215.26   $215.25   $215.30  
  Purchase #2 $21.32   9.538%   $23.3535   $23.35   $23.35   $23.40  
  Purchase #3 $91.64   8.421%   $99.357   $99.36   $99.35   $99.40  
  Purchase #4 $193.44   4.402%   $201.9552   $201.96   $201.95   $202.00  
  Purchase #5 $7.30   7.407%   $7.8407   $7.84   $7.85   $7.80  
  Purchase #6 $39.53   8.828%   $43.0197   $43.02   $43.00   $43.00  
  Purchase #7 $202.60   7.400%   $217.5924   $217.59   $217.60   $217.60  
  7 purchase totals = $758.28       $808.3735   $808.38   $808.35   $808.50