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 $77.58   13.662%   $88.179   $88.18   $88.20   $88.20  
  Purchase #2 $73.50   3.737%   $76.2467   $76.25   $76.25   $76.20  
  Purchase #3 $197.69   8.359%   $214.2149   $214.21   $214.20   $214.20  
  Purchase #4 $177.98   12.694%   $200.5728   $200.57   $200.55   $200.60  
  Purchase #5 $200.96   7.242%   $215.5135   $215.51   $215.50   $215.50  
  Purchase #6 $73.37   7.600%   $78.9461   $78.95   $78.95   $78.90  
  Purchase #7 $172.66   12.732%   $194.6431   $194.64   $194.65   $194.60  
  7 purchase totals = $973.74       $1,068.3161   $1,068.31   $1,068.30   $1,068.20