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   9.446%   $224.0688   $224.07   $224.05   $224.10  
  Purchase #2 $238.34   6.398%   $253.589   $253.59   $253.60   $253.60  
  Purchase #3 $74.86   4.345%   $78.1127   $78.11   $78.10   $78.10  
  Purchase #4 $49.84   12.726%   $56.1826   $56.18   $56.20   $56.20  
  Purchase #5 $247.48   4.651%   $258.9903   $258.99   $259.00   $259.00  
  Purchase #6 $13.85   3.108%   $14.2805   $14.28   $14.30   $14.30  
  Purchase #7 $162.78   7.767%   $175.4231   $175.42   $175.40   $175.40  
  7 purchase totals = $991.88       $1,060.6470   $1,060.64   $1,060.65   $1,060.70