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 $168.80   13.571%   $191.7078   $191.71   $191.70   $191.70  
  Purchase #2 $98.79   11.786%   $110.4334   $110.43   $110.45   $110.40  
  Purchase #3 $54.60   3.236%   $56.3669   $56.37   $56.35   $56.40  
  Purchase #4 $167.66   4.753%   $175.6289   $175.63   $175.65   $175.60  
  Purchase #5 $148.97   9.298%   $162.8212   $162.82   $162.80   $162.80  
  Purchase #6 $132.89   4.164%   $138.4235   $138.42   $138.40   $138.40  
  Purchase #7 $199.66   7.794%   $215.2215   $215.22   $215.20   $215.20  
  7 purchase totals = $971.37       $1,050.6032   $1,050.60   $1,050.55   $1,050.50