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 $182.42   13.551%   $207.1397   $207.14   $207.15   $207.10  
  Purchase #2 $203.37   12.364%   $228.5147   $228.51   $228.50   $228.50  
  Purchase #3 $122.57   8.496%   $132.9835   $132.98   $133.00   $133.00  
  Purchase #4 $168.79   8.393%   $182.9565   $182.96   $182.95   $183.00  
  Purchase #5 $200.63   4.433%   $209.5239   $209.52   $209.50   $209.50  
  Purchase #6 $47.72   8.134%   $51.6015   $51.60   $51.60   $51.60  
  Purchase #7 $45.50   3.335%   $47.0174   $47.02   $47.00   $47.00  
  7 purchase totals = $971.00       $1,059.7372   $1,059.73   $1,059.70   $1,059.70