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 $232.91   11.420%   $259.5083   $259.51   $259.50   $259.50  
  Purchase #2 $22.81   5.233%   $24.0036   $24.00   $24.00   $24.00  
  Purchase #3 $194.30   7.676%   $209.2145   $209.21   $209.20   $209.20  
  Purchase #4 $5.36   5.171%   $5.6372   $5.64   $5.65   $5.60  
  Purchase #5 $129.82   4.525%   $135.6944   $135.69   $135.70   $135.70  
  Purchase #6 $174.28   8.700%   $189.4424   $189.44   $189.45   $189.40  
  Purchase #7 $203.32   7.145%   $217.8472   $217.85   $217.85   $217.80  
  7 purchase totals = $962.80       $1,041.3476   $1,041.34   $1,041.35   $1,041.20