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 $244.98   11.851%   $274.0126   $274.01   $274.00   $274.00  
  Purchase #2 $48.79   5.834%   $51.6364   $51.64   $51.65   $51.60  
  Purchase #3 $243.77   5.865%   $258.0671   $258.07   $258.05   $258.10  
  Purchase #4 $225.53   5.469%   $237.8642   $237.86   $237.85   $237.90  
  Purchase #5 $215.91   7.704%   $232.5437   $232.54   $232.55   $232.50  
  Purchase #6 $169.26   13.261%   $191.7056   $191.71   $191.70   $191.70  
  Purchase #7 $218.86   5.481%   $230.8557   $230.86   $230.85   $230.90  
  7 purchase totals = $1,367.10       $1,476.6853   $1,476.69   $1,476.65   $1,476.70