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 $41.73   12.228%   $46.8327   $46.83   $46.85   $46.80  
  Purchase #2 $227.49   7.356%   $244.2242   $244.22   $244.20   $244.20  
  Purchase #3 $245.65   11.838%   $274.73   $274.73   $274.75   $274.70  
  Purchase #4 $53.39   6.135%   $56.6655   $56.67   $56.65   $56.70  
  Purchase #5 $229.58   3.481%   $237.5717   $237.57   $237.55   $237.60  
  Purchase #6 $244.71   9.464%   $267.8694   $267.87   $267.85   $267.90  
  Purchase #7 $191.59   11.307%   $213.2531   $213.25   $213.25   $213.30  
  7 purchase totals = $1,234.14       $1,341.1466   $1,341.14   $1,341.10   $1,341.20