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 $240.45   4.665%   $251.667   $251.67   $251.65   $251.70  
  Purchase #2 $107.33   6.186%   $113.9694   $113.97   $113.95   $114.00  
  Purchase #3 $184.93   9.749%   $202.9588   $202.96   $202.95   $203.00  
  Purchase #4 $153.93   9.413%   $168.4194   $168.42   $168.40   $168.40  
  Purchase #5 $32.87   8.642%   $35.7106   $35.71   $35.70   $35.70  
  Purchase #6 $197.82   5.249%   $208.2036   $208.20   $208.20   $208.20  
  Purchase #7 $58.85   9.400%   $64.3819   $64.38   $64.40   $64.40  
  7 purchase totals = $976.18       $1,045.3107   $1,045.31   $1,045.25   $1,045.40