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 $140.98   7.623%   $151.7269   $151.73   $151.75   $151.70  
  Purchase #2 $174.67   8.826%   $190.0864   $190.09   $190.10   $190.10  
  Purchase #3 $171.76   8.157%   $185.7705   $185.77   $185.75   $185.80  
  Purchase #4 $204.56   7.128%   $219.141   $219.14   $219.15   $219.10  
  Purchase #5 $114.93   7.842%   $123.9428   $123.94   $123.95   $123.90  
  Purchase #6 $125.53   11.505%   $139.9722   $139.97   $139.95   $140.00  
  Purchase #7 $63.96   6.867%   $68.3521   $68.35   $68.35   $68.40  
  7 purchase totals = $996.39       $1,078.9919   $1,078.99   $1,079.00   $1,079.00