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 $232.56   12.809%   $262.3486   $262.35   $262.35   $262.30  
  Purchase #2 $110.62   6.436%   $117.7395   $117.74   $117.75   $117.70  
  Purchase #3 $58.68   13.828%   $66.7943   $66.79   $66.80   $66.80  
  Purchase #4 $236.71   13.782%   $269.3334   $269.33   $269.35   $269.30  
  Purchase #5 $101.72   11.479%   $113.3964   $113.40   $113.40   $113.40  
  Purchase #6 $98.42   8.169%   $106.4599   $106.46   $106.45   $106.50  
  Purchase #7 $184.53   10.852%   $204.5552   $204.56   $204.55   $204.60  
  7 purchase totals = $1,023.24       $1,140.6273   $1,140.63   $1,140.65   $1,140.60