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 $232.32   5.420%   $244.9117   $244.91   $244.90   $244.90  
  Purchase #2 $149.39   4.174%   $155.6255   $155.63   $155.65   $155.60  
  Purchase #3 $225.85   9.410%   $247.1025   $247.10   $247.10   $247.10  
  Purchase #4 $196.86   10.319%   $217.174   $217.17   $217.15   $217.20  
  Purchase #5 $110.97   4.777%   $116.271   $116.27   $116.25   $116.30  
  Purchase #6 $28.82   4.191%   $30.0278   $30.03   $30.05   $30.00  
  Purchase #7 $212.41   8.506%   $230.4776   $230.48   $230.50   $230.50  
  7 purchase totals = $1,156.62       $1,241.5901   $1,241.59   $1,241.60   $1,241.60