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 $242.66   9.123%   $264.7979   $264.80   $264.80   $264.80  
  Purchase #2 $188.90   7.462%   $202.9957   $203.00   $203.00   $203.00  
  Purchase #3 $149.70   7.862%   $161.4694   $161.47   $161.45   $161.50  
  Purchase #4 $132.28   13.574%   $150.2357   $150.24   $150.25   $150.20  
  Purchase #5 $81.91   4.300%   $85.4321   $85.43   $85.45   $85.40  
  Purchase #6 $240.95   5.214%   $253.5131   $253.51   $253.50   $253.50  
  Purchase #7 $218.83   11.189%   $243.3149   $243.31   $243.30   $243.30  
  7 purchase totals = $1,255.23       $1,361.7588   $1,361.76   $1,361.75   $1,361.70