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 $245.98   5.432%   $259.3416   $259.34   $259.35   $259.30  
  Purchase #2 $10.93   11.425%   $12.1788   $12.18   $12.20   $12.20  
  Purchase #3 $145.82   5.257%   $153.4858   $153.49   $153.50   $153.50  
  Purchase #4 $230.99   4.699%   $241.8442   $241.84   $241.85   $241.80  
  Purchase #5 $222.38   13.480%   $252.3568   $252.36   $252.35   $252.40  
  Purchase #6 $134.92   10.839%   $149.544   $149.54   $149.55   $149.50  
  Purchase #7 $151.61   13.762%   $172.4746   $172.47   $172.45   $172.50  
  7 purchase totals = $1,142.63       $1,241.2258   $1,241.22   $1,241.25   $1,241.20