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 $96.96   7.374%   $104.1098   $104.11   $104.10   $104.10  
  Purchase #2 $197.97   4.687%   $207.2489   $207.25   $207.25   $207.20  
  Purchase #3 $79.72   13.154%   $90.2064   $90.21   $90.20   $90.20  
  Purchase #4 $169.73   10.243%   $187.1154   $187.12   $187.10   $187.10  
  Purchase #5 $7.65   12.869%   $8.6345   $8.63   $8.65   $8.60  
  Purchase #6 $200.56   12.117%   $224.8619   $224.86   $224.85   $224.90  
  Purchase #7 $116.67   5.813%   $123.452   $123.45   $123.45   $123.50  
  7 purchase totals = $869.26       $945.6289   $945.63   $945.60   $945.60