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 $236.92   11.287%   $263.6612   $263.66   $263.65   $263.70  
  Purchase #2 $97.89   5.124%   $102.9059   $102.91   $102.90   $102.90  
  Purchase #3 $118.44   4.378%   $123.6253   $123.63   $123.65   $123.60  
  Purchase #4 $224.48   9.654%   $246.1513   $246.15   $246.15   $246.20  
  Purchase #5 $212.97   11.597%   $237.6681   $237.67   $237.65   $237.70  
  Purchase #6 $171.46   5.172%   $180.3279   $180.33   $180.35   $180.30  
  Purchase #7 $137.39   9.481%   $150.4159   $150.42   $150.40   $150.40  
  7 purchase totals = $1,199.55       $1,304.7556   $1,304.77   $1,304.75   $1,304.80