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 $71.71   8.629%   $77.8979   $77.90   $77.90   $77.90  
  Purchase #2 $224.50   6.754%   $239.6627   $239.66   $239.65   $239.70  
  Purchase #3 $196.60   4.567%   $205.5787   $205.58   $205.60   $205.60  
  Purchase #4 $206.46   12.322%   $231.9   $231.90   $231.90   $231.90  
  Purchase #5 $159.78   6.118%   $169.5553   $169.56   $169.55   $169.60  
  Purchase #6 $24.83   9.396%   $27.163   $27.16   $27.15   $27.20  
  Purchase #7 $250.46   6.670%   $267.1657   $267.17   $267.15   $267.20  
  7 purchase totals = $1,134.34       $1,218.9233   $1,218.93   $1,218.90   $1,219.10