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 $58.57   12.364%   $65.8116   $65.81   $65.80   $65.80  
  Purchase #2 $200.89   7.616%   $216.1898   $216.19   $216.20   $216.20  
  Purchase #3 $237.31   3.160%   $244.809   $244.81   $244.80   $244.80  
  Purchase #4 $139.59   12.231%   $156.6633   $156.66   $156.65   $156.70  
  Purchase #5 $216.64   6.746%   $231.2545   $231.25   $231.25   $231.30  
  Purchase #6 $102.79   13.481%   $116.6471   $116.65   $116.65   $116.60  
  Purchase #7 $213.66   13.550%   $242.6109   $242.61   $242.60   $242.60  
  7 purchase totals = $1,169.45       $1,273.9862   $1,273.98   $1,273.95   $1,274.00