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 $243.96   6.315%   $259.3661   $259.37   $259.35   $259.40  
  Purchase #2 $168.79   8.300%   $182.7996   $182.80   $182.80   $182.80  
  Purchase #3 $188.82   6.695%   $201.4615   $201.46   $201.45   $201.50  
  Purchase #4 $35.71   7.728%   $38.4697   $38.47   $38.45   $38.50  
  Purchase #5 $11.38   7.465%   $12.2295   $12.23   $12.25   $12.20  
  Purchase #6 $241.92   13.674%   $275.0001   $275.00   $275.00   $275.00  
  Purchase #7 $160.82   8.183%   $173.9799   $173.98   $174.00   $174.00  
  7 purchase totals = $1,051.40       $1,143.3064   $1,143.31   $1,143.30   $1,143.40