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 $113.63   11.571%   $126.7781   $126.78   $126.80   $126.80  
  Purchase #2 $96.53   6.104%   $102.4222   $102.42   $102.40   $102.40  
  Purchase #3 $171.95   5.690%   $181.734   $181.73   $181.75   $181.70  
  Purchase #4 $166.48   12.151%   $186.709   $186.71   $186.70   $186.70  
  Purchase #5 $236.29   5.467%   $249.208   $249.21   $249.20   $249.20  
  Purchase #6 $135.90   9.488%   $148.7942   $148.79   $148.80   $148.80  
  Purchase #7 $72.86   10.439%   $80.4659   $80.47   $80.45   $80.50  
  7 purchase totals = $993.64       $1,076.1114   $1,076.11   $1,076.10   $1,076.10