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 $116.84   13.841%   $133.0118   $133.01   $133.00   $133.00  
  Purchase #2 $224.62   7.435%   $241.3205   $241.32   $241.30   $241.30  
  Purchase #3 $63.58   7.441%   $68.311   $68.31   $68.30   $68.30  
  Purchase #4 $110.43   13.110%   $124.9074   $124.91   $124.90   $124.90  
  Purchase #5 $225.35   13.130%   $254.9385   $254.94   $254.95   $254.90  
  Purchase #6 $170.94   13.257%   $193.6015   $193.60   $193.60   $193.60  
  Purchase #7 $209.93   5.403%   $221.2725   $221.27   $221.25   $221.30  
  7 purchase totals = $1,121.69       $1,237.3632   $1,237.36   $1,237.30   $1,237.30