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 $114.91   8.474%   $124.6475   $124.65   $124.65   $124.60  
  Purchase #2 $174.97   8.239%   $189.3858   $189.39   $189.40   $189.40  
  Purchase #3 $242.85   9.506%   $265.9353   $265.94   $265.95   $265.90  
  Purchase #4 $167.66   3.317%   $173.2213   $173.22   $173.20   $173.20  
  Purchase #5 $59.39   3.715%   $61.5963   $61.60   $61.60   $61.60  
  Purchase #6 $219.52   13.117%   $248.3144   $248.31   $248.30   $248.30  
  Purchase #7 $77.83   13.484%   $88.3246   $88.32   $88.30   $88.30  
  7 purchase totals = $1,057.13       $1,151.4252   $1,151.43   $1,151.40   $1,151.30