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 $204.73   5.596%   $216.1867   $216.19   $216.20   $216.20  
  Purchase #2 $186.39   4.535%   $194.8428   $194.84   $194.85   $194.80  
  Purchase #3 $159.31   7.817%   $171.7633   $171.76   $171.75   $171.80  
  Purchase #4 $42.33   6.303%   $44.9981   $45.00   $45.00   $45.00  
  Purchase #5 $88.27   11.276%   $98.2233   $98.22   $98.20   $98.20  
  Purchase #6 $250.92   3.376%   $259.3911   $259.39   $259.40   $259.40  
  Purchase #7 $41.57   6.850%   $44.4175   $44.42   $44.40   $44.40  
  7 purchase totals = $973.52       $1,029.8228   $1,029.82   $1,029.80   $1,029.80