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 $53.92   9.357%   $58.9653   $58.97   $58.95   $59.00  
  Purchase #2 $108.82   11.597%   $121.4399   $121.44   $121.45   $121.40  
  Purchase #3 $107.47   13.123%   $121.5733   $121.57   $121.55   $121.60  
  Purchase #4 $143.41   6.179%   $152.2713   $152.27   $152.25   $152.30  
  Purchase #5 $220.49   11.726%   $246.3447   $246.34   $246.35   $246.30  
  Purchase #6 $146.70   3.525%   $151.8712   $151.87   $151.85   $151.90  
  Purchase #7 $230.82   13.815%   $262.7078   $262.71   $262.70   $262.70  
  7 purchase totals = $1,011.63       $1,115.1735   $1,115.17   $1,115.10   $1,115.20