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 $108.82   6.658%   $116.0652   $116.07   $116.05   $116.10  
  Purchase #2 $14.92   11.273%   $16.6019   $16.60   $16.60   $16.60  
  Purchase #3 $138.72   6.828%   $148.1918   $148.19   $148.20   $148.20  
  Purchase #4 $32.84   6.246%   $34.8912   $34.89   $34.90   $34.90  
  Purchase #5 $184.92   11.333%   $205.877   $205.88   $205.90   $205.90  
  Purchase #6 $52.68   11.824%   $58.9089   $58.91   $58.90   $58.90  
  Purchase #7 $141.34   6.574%   $150.6317   $150.63   $150.65   $150.60  
  7 purchase totals = $674.24       $731.1677   $731.17   $731.20   $731.20