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 $82.56   11.618%   $92.1518   $92.15   $92.15   $92.20  
  Purchase #2 $43.48   6.515%   $46.3127   $46.31   $46.30   $46.30  
  Purchase #3 $111.90   9.719%   $122.7756   $122.78   $122.80   $122.80  
  Purchase #4 $235.98   11.445%   $262.9879   $262.99   $263.00   $263.00  
  Purchase #5 $159.90   11.492%   $178.2757   $178.28   $178.30   $178.30  
  Purchase #6 $169.40   10.630%   $187.4072   $187.41   $187.40   $187.40  
  Purchase #7 $202.36   11.409%   $225.4473   $225.45   $225.45   $225.40  
  7 purchase totals = $1,005.58       $1,115.3582   $1,115.37   $1,115.40   $1,115.40