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 $94.71   12.573%   $106.6179   $106.62   $106.60   $106.60  
  Purchase #2 $185.73   6.520%   $197.8396   $197.84   $197.85   $197.80  
  Purchase #3 $8.82   9.208%   $9.6321   $9.63   $9.65   $9.60  
  Purchase #4 $179.42   12.720%   $202.2422   $202.24   $202.25   $202.20  
  Purchase #5 $117.57   12.269%   $131.9947   $131.99   $132.00   $132.00  
  Purchase #6 $197.30   12.749%   $222.4538   $222.45   $222.45   $222.50  
  Purchase #7 $207.94   13.200%   $235.3881   $235.39   $235.40   $235.40  
  7 purchase totals = $991.49       $1,106.1684   $1,106.16   $1,106.20   $1,106.10