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 $67.61   12.119%   $75.8037   $75.80   $75.80   $75.80  
  Purchase #2 $235.89   13.676%   $268.1503   $268.15   $268.15   $268.20  
  Purchase #3 $23.85   13.620%   $27.0984   $27.10   $27.10   $27.10  
  Purchase #4 $213.84   11.402%   $238.222   $238.22   $238.20   $238.20  
  Purchase #5 $204.57   11.314%   $227.715   $227.72   $227.70   $227.70  
  Purchase #6 $119.49   4.191%   $124.4978   $124.50   $124.50   $124.50  
  Purchase #7 $162.96   4.724%   $170.6582   $170.66   $170.65   $170.70  
  7 purchase totals = $1,028.21       $1,132.1454   $1,132.15   $1,132.10   $1,132.20