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 $243.33   10.561%   $269.0281   $269.03   $269.05   $269.00  
  Purchase #2 $191.62   5.431%   $202.0269   $202.03   $202.05   $202.00  
  Purchase #3 $169.39   11.735%   $189.2679   $189.27   $189.25   $189.30  
  Purchase #4 $74.49   3.156%   $76.8409   $76.84   $76.85   $76.80  
  Purchase #5 $6.95   4.672%   $7.2747   $7.27   $7.25   $7.30  
  Purchase #6 $184.66   5.427%   $194.6815   $194.68   $194.70   $194.70  
  Purchase #7 $194.97   3.324%   $201.4508   $201.45   $201.45   $201.50  
  7 purchase totals = $1,065.41       $1,140.5708   $1,140.57   $1,140.60   $1,140.60