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 $204.72   9.759%   $224.6986   $224.70   $224.70   $224.70  
  Purchase #2 $87.31   9.235%   $95.3731   $95.37   $95.35   $95.40  
  Purchase #3 $242.53   12.547%   $272.9602   $272.96   $272.95   $273.00  
  Purchase #4 $226.55   10.492%   $250.3196   $250.32   $250.30   $250.30  
  Purchase #5 $175.78   4.316%   $183.3667   $183.37   $183.35   $183.40  
  Purchase #6 $122.99   7.117%   $131.7432   $131.74   $131.75   $131.70  
  Purchase #7 $219.27   6.181%   $232.8231   $232.82   $232.80   $232.80  
  7 purchase totals = $1,279.15       $1,391.2845   $1,391.28   $1,391.20   $1,391.30