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 $191.36   6.693%   $204.1677   $204.17   $204.15   $204.20  
  Purchase #2 $93.38   11.744%   $104.3465   $104.35   $104.35   $104.30  
  Purchase #3 $231.95   8.531%   $251.7377   $251.74   $251.75   $251.70  
  Purchase #4 $5.45   6.271%   $5.7918   $5.79   $5.80   $5.80  
  Purchase #5 $54.51   10.449%   $60.2057   $60.21   $60.20   $60.20  
  Purchase #6 $107.70   13.641%   $122.3914   $122.39   $122.40   $122.40  
  Purchase #7 $9.29   5.377%   $9.7895   $9.79   $9.80   $9.80  
  7 purchase totals = $693.64       $758.4303   $758.44   $758.45   $758.40