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 $250.73   10.400%   $276.8059   $276.81   $276.80   $276.80  
  Purchase #2 $147.84   8.763%   $160.7952   $160.80   $160.80   $160.80  
  Purchase #3 $227.56   8.131%   $246.0629   $246.06   $246.05   $246.10  
  Purchase #4 $40.81   13.819%   $46.4495   $46.45   $46.45   $46.40  
  Purchase #5 $83.66   4.644%   $87.5452   $87.55   $87.55   $87.50  
  Purchase #6 $15.83   13.457%   $17.9602   $17.96   $17.95   $18.00  
  Purchase #7 $200.53   6.731%   $214.0277   $214.03   $214.05   $214.00  
  7 purchase totals = $966.96       $1,049.6466   $1,049.66   $1,049.65   $1,049.60