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 $246.88   4.110%   $257.0268   $257.03   $257.05   $257.00  
  Purchase #2 $141.43   5.327%   $148.964   $148.96   $148.95   $149.00  
  Purchase #3 $13.79   4.426%   $14.4003   $14.40   $14.40   $14.40  
  Purchase #4 $51.98   7.285%   $55.7667   $55.77   $55.75   $55.80  
  Purchase #5 $182.35   12.280%   $204.7426   $204.74   $204.75   $204.70  
  Purchase #6 $195.53   9.435%   $213.9783   $213.98   $214.00   $214.00  
  Purchase #7 $135.51   13.665%   $154.0274   $154.03   $154.05   $154.00  
  7 purchase totals = $967.47       $1,048.9061   $1,048.91   $1,048.95   $1,048.90