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 $163.31   3.608%   $169.2022   $169.20   $169.20   $169.20  
  Purchase #2 $141.90   13.836%   $161.5333   $161.53   $161.55   $161.50  
  Purchase #3 $129.42   6.139%   $137.3651   $137.37   $137.35   $137.40  
  Purchase #4 $237.64   11.586%   $265.173   $265.17   $265.15   $265.20  
  Purchase #5 $181.26   12.137%   $203.2595   $203.26   $203.25   $203.30  
  Purchase #6 $48.27   12.868%   $54.4814   $54.48   $54.50   $54.50  
  Purchase #7 $66.81   3.166%   $68.9252   $68.93   $68.95   $68.90  
  7 purchase totals = $968.61       $1,059.9397   $1,059.94   $1,059.95   $1,060.00