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 $141.43   8.134%   $152.9339   $152.93   $152.95   $152.90  
  Purchase #2 $171.82   5.595%   $181.4333   $181.43   $181.45   $181.40  
  Purchase #3 $213.68   5.560%   $225.5606   $225.56   $225.55   $225.60  
  Purchase #4 $191.41   3.724%   $198.5381   $198.54   $198.55   $198.50  
  Purchase #5 $242.43   10.347%   $267.5142   $267.51   $267.50   $267.50  
  Purchase #6 $231.94   7.751%   $249.9177   $249.92   $249.90   $249.90  
  Purchase #7 $225.84   13.765%   $256.9269   $256.93   $256.95   $256.90  
  7 purchase totals = $1,418.55       $1,532.8247   $1,532.82   $1,532.85   $1,532.70