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 $69.78   5.839%   $73.8545   $73.85   $73.85   $73.90  
  Purchase #2 $189.74   12.396%   $213.2602   $213.26   $213.25   $213.30  
  Purchase #3 $235.51   9.436%   $257.7327   $257.73   $257.75   $257.70  
  Purchase #4 $237.65   5.571%   $250.8895   $250.89   $250.90   $250.90  
  Purchase #5 $97.69   6.428%   $103.9695   $103.97   $103.95   $104.00  
  Purchase #6 $164.79   12.239%   $184.9586   $184.96   $184.95   $185.00  
  Purchase #7 $87.84   9.131%   $95.8607   $95.86   $95.85   $95.90  
  7 purchase totals = $1,083.00       $1,180.5257   $1,180.52   $1,180.50   $1,180.70