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 $211.85   3.652%   $219.5868   $219.59   $219.60   $219.60  
  Purchase #2 $53.77   13.132%   $60.8311   $60.83   $60.85   $60.80  
  Purchase #3 $96.76   11.586%   $107.9706   $107.97   $107.95   $108.00  
  Purchase #4 $231.57   11.417%   $258.0083   $258.01   $258.00   $258.00  
  Purchase #5 $50.43   13.428%   $57.2017   $57.20   $57.20   $57.20  
  Purchase #6 $11.94   9.330%   $13.054   $13.05   $13.05   $13.10  
  Purchase #7 $71.89   12.443%   $80.8353   $80.84   $80.85   $80.80  
  7 purchase totals = $728.21       $797.4878   $797.49   $797.50   $797.50