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 $244.36   13.112%   $276.4005   $276.40   $276.40   $276.40  
  Purchase #2 $26.30   9.676%   $28.8448   $28.84   $28.85   $28.80  
  Purchase #3 $243.50   8.419%   $264.0003   $264.00   $264.00   $264.00  
  Purchase #4 $142.78   6.634%   $152.252   $152.25   $152.25   $152.30  
  Purchase #5 $199.57   9.471%   $218.4713   $218.47   $218.45   $218.50  
  Purchase #6 $246.94   11.505%   $275.3504   $275.35   $275.35   $275.40  
  Purchase #7 $19.97   8.204%   $21.6083   $21.61   $21.60   $21.60  
  7 purchase totals = $1,123.42       $1,236.9276   $1,236.92   $1,236.90   $1,237.00