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 $53.57   12.827%   $60.4414   $60.44   $60.45   $60.40  
  Purchase #2 $218.85   12.639%   $246.5105   $246.51   $246.50   $246.50  
  Purchase #3 $240.62   6.281%   $255.7333   $255.73   $255.75   $255.70  
  Purchase #4 $179.95   3.841%   $186.8619   $186.86   $186.85   $186.90  
  Purchase #5 $78.55   10.778%   $87.0161   $87.02   $87.00   $87.00  
  Purchase #6 $83.58   9.757%   $91.7349   $91.73   $91.75   $91.70  
  Purchase #7 $128.78   7.669%   $138.6561   $138.66   $138.65   $138.70  
  7 purchase totals = $983.90       $1,066.9542   $1,066.95   $1,066.95   $1,066.90