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 $186.84   5.593%   $197.29   $197.29   $197.30   $197.30  
  Purchase #2 $29.81   6.637%   $31.7885   $31.79   $31.80   $31.80  
  Purchase #3 $147.89   5.163%   $155.5256   $155.53   $155.55   $155.50  
  Purchase #4 $150.74   7.806%   $162.5068   $162.51   $162.50   $162.50  
  Purchase #5 $26.71   6.185%   $28.362   $28.36   $28.35   $28.40  
  Purchase #6 $7.30   11.435%   $8.1348   $8.13   $8.15   $8.10  
  Purchase #7 $166.34   5.327%   $175.2009   $175.20   $175.20   $175.20  
  7 purchase totals = $715.63       $758.8086   $758.81   $758.85   $758.80