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 $54.42   5.289%   $57.2983   $57.30   $57.30   $57.30  
  Purchase #2 $146.94   4.583%   $153.6743   $153.67   $153.65   $153.70  
  Purchase #3 $71.62   12.529%   $80.5933   $80.59   $80.60   $80.60  
  Purchase #4 $214.62   4.740%   $224.793   $224.79   $224.80   $224.80  
  Purchase #5 $213.68   6.689%   $227.9731   $227.97   $227.95   $228.00  
  Purchase #6 $250.73   10.183%   $276.2618   $276.26   $276.25   $276.30  
  Purchase #7 $171.73   10.474%   $189.717   $189.72   $189.70   $189.70  
  7 purchase totals = $1,123.74       $1,210.3108   $1,210.30   $1,210.25   $1,210.40