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 $212.54   6.589%   $226.5443   $226.54   $226.55   $226.50  
  Purchase #2 $19.99   13.314%   $22.6515   $22.65   $22.65   $22.70  
  Purchase #3 $152.97   10.804%   $169.4969   $169.50   $169.50   $169.50  
  Purchase #4 $232.57   13.291%   $263.4809   $263.48   $263.50   $263.50  
  Purchase #5 $61.89   4.218%   $64.5005   $64.50   $64.50   $64.50  
  Purchase #6 $195.35   4.475%   $204.0919   $204.09   $204.10   $204.10  
  Purchase #7 $200.69   11.641%   $224.0523   $224.05   $224.05   $224.10  
  7 purchase totals = $1,076.00       $1,174.8183   $1,174.81   $1,174.85   $1,174.90