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 $59.96   13.278%   $67.9215   $67.92   $67.90   $67.90  
  Purchase #2 $235.78   3.226%   $243.3863   $243.39   $243.40   $243.40  
  Purchase #3 $148.68   9.328%   $162.5489   $162.55   $162.55   $162.50  
  Purchase #4 $217.79   9.826%   $239.19   $239.19   $239.20   $239.20  
  Purchase #5 $62.79   11.790%   $70.1929   $70.19   $70.20   $70.20  
  Purchase #6 $172.93   5.481%   $182.4083   $182.41   $182.40   $182.40  
  Purchase #7 $57.79   12.644%   $65.097   $65.10   $65.10   $65.10  
  7 purchase totals = $955.72       $1,030.7449   $1,030.75   $1,030.75   $1,030.70