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 $210.59   12.498%   $236.9095   $236.91   $236.90   $236.90  
  Purchase #2 $239.86   9.583%   $262.8458   $262.85   $262.85   $262.80  
  Purchase #3 $198.65   13.511%   $225.4896   $225.49   $225.50   $225.50  
  Purchase #4 $92.45   11.795%   $103.3545   $103.35   $103.35   $103.40  
  Purchase #5 $36.61   8.596%   $39.757   $39.76   $39.75   $39.80  
  Purchase #6 $144.52   10.854%   $160.2062   $160.21   $160.20   $160.20  
  Purchase #7 $28.57   10.318%   $31.5179   $31.52   $31.50   $31.50  
  7 purchase totals = $951.25       $1,060.0805   $1,060.09   $1,060.05   $1,060.10