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 $126.53   3.323%   $130.7346   $130.73   $130.75   $130.70  
  Purchase #2 $187.95   4.529%   $196.4623   $196.46   $196.45   $196.50  
  Purchase #3 $52.92   4.564%   $55.3353   $55.34   $55.35   $55.30  
  Purchase #4 $23.48   9.787%   $25.778   $25.78   $25.80   $25.80  
  Purchase #5 $239.70   12.157%   $268.8403   $268.84   $268.85   $268.80  
  Purchase #6 $152.73   11.318%   $170.016   $170.02   $170.00   $170.00  
  Purchase #7 $163.78   5.751%   $173.199   $173.20   $173.20   $173.20  
  7 purchase totals = $947.09       $1,020.3655   $1,020.37   $1,020.40   $1,020.30