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 $47.84   7.674%   $51.5112   $51.51   $51.50   $51.50  
  Purchase #2 $41.92   3.233%   $43.2753   $43.28   $43.30   $43.30  
  Purchase #3 $201.91   8.760%   $219.5973   $219.60   $219.60   $219.60  
  Purchase #4 $195.26   6.785%   $208.5084   $208.51   $208.50   $208.50  
  Purchase #5 $218.77   12.586%   $246.3044   $246.30   $246.30   $246.30  
  Purchase #6 $193.41   5.547%   $204.1385   $204.14   $204.15   $204.10  
  Purchase #7 $93.86   10.789%   $103.9866   $103.99   $104.00   $104.00  
  7 purchase totals = $992.97       $1,077.3217   $1,077.33   $1,077.35   $1,077.30