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 $49.46   9.542%   $54.1795   $54.18   $54.20   $54.20  
  Purchase #2 $245.94   8.331%   $266.4293   $266.43   $266.45   $266.40  
  Purchase #3 $80.76   5.165%   $84.9313   $84.93   $84.95   $84.90  
  Purchase #4 $92.63   11.325%   $103.1203   $103.12   $103.10   $103.10  
  Purchase #5 $131.63   3.156%   $135.7842   $135.78   $135.80   $135.80  
  Purchase #6 $125.88   12.678%   $141.8391   $141.84   $141.85   $141.80  
  Purchase #7 $216.31   5.277%   $227.7247   $227.72   $227.70   $227.70  
  7 purchase totals = $942.61       $1,014.0084   $1,014.00   $1,014.05   $1,013.90