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 $185.82   11.792%   $207.7319   $207.73   $207.75   $207.70  
  Purchase #2 $29.81   13.518%   $33.8397   $33.84   $33.85   $33.80  
  Purchase #3 $188.92   9.152%   $206.21   $206.21   $206.20   $206.20  
  Purchase #4 $46.82   13.391%   $53.0897   $53.09   $53.10   $53.10  
  Purchase #5 $189.74   10.257%   $209.2016   $209.20   $209.20   $209.20  
  Purchase #6 $227.72   8.400%   $246.8485   $246.85   $246.85   $246.80  
  Purchase #7 $183.25   7.500%   $196.9938   $196.99   $197.00   $197.00  
  7 purchase totals = $1,052.08       $1,153.9152   $1,153.91   $1,153.95   $1,153.80