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 $209.48   10.589%   $231.6618   $231.66   $231.65   $231.70  
  Purchase #2 $202.46   11.373%   $225.4858   $225.49   $225.50   $225.50  
  Purchase #3 $26.92   6.429%   $28.6507   $28.65   $28.65   $28.70  
  Purchase #4 $234.70   12.695%   $264.4952   $264.50   $264.50   $264.50  
  Purchase #5 $186.26   11.462%   $207.6091   $207.61   $207.60   $207.60  
  Purchase #6 $246.46   11.388%   $274.5269   $274.53   $274.55   $274.50  
  Purchase #7 $39.86   5.665%   $42.1181   $42.12   $42.10   $42.10  
  7 purchase totals = $1,146.14       $1,274.5476   $1,274.56   $1,274.55   $1,274.60