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 $211.97   12.163%   $237.7519   $237.75   $237.75   $237.80  
  Purchase #2 $200.47   12.660%   $225.8495   $225.85   $225.85   $225.80  
  Purchase #3 $57.33   5.256%   $60.3433   $60.34   $60.35   $60.30  
  Purchase #4 $235.55   5.711%   $249.0023   $249.00   $249.00   $249.00  
  Purchase #5 $58.80   9.536%   $64.4072   $64.41   $64.40   $64.40  
  Purchase #6 $130.68   3.130%   $134.7703   $134.77   $134.75   $134.80  
  Purchase #7 $134.56   6.356%   $143.1126   $143.11   $143.10   $143.10  
  7 purchase totals = $1,029.36       $1,115.2371   $1,115.23   $1,115.20   $1,115.20