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 $116.71   12.541%   $131.3466   $131.35   $131.35   $131.30  
  Purchase #2 $112.30   9.323%   $122.7697   $122.77   $122.75   $122.80  
  Purchase #3 $77.75   10.413%   $85.8461   $85.85   $85.85   $85.80  
  Purchase #4 $144.73   5.189%   $152.24   $152.24   $152.25   $152.20  
  Purchase #5 $152.84   3.791%   $158.6342   $158.63   $158.65   $158.60  
  Purchase #6 $109.33   6.221%   $116.1314   $116.13   $116.15   $116.10  
  Purchase #7 $232.76   11.693%   $259.9766   $259.98   $260.00   $260.00  
  7 purchase totals = $946.42       $1,026.9446   $1,026.95   $1,027.00   $1,026.80