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 $246.57   11.381%   $274.6321   $274.63   $274.65   $274.60  
  Purchase #2 $182.29   4.336%   $190.1941   $190.19   $190.20   $190.20  
  Purchase #3 $191.52   7.717%   $206.2996   $206.30   $206.30   $206.30  
  Purchase #4 $52.99   9.183%   $57.8561   $57.86   $57.85   $57.90  
  Purchase #5 $243.74   10.464%   $269.245   $269.25   $269.25   $269.20  
  Purchase #6 $231.64   13.504%   $262.9207   $262.92   $262.90   $262.90  
  Purchase #7 $205.25   7.460%   $220.5617   $220.56   $220.55   $220.60  
  7 purchase totals = $1,354.00       $1,481.7093   $1,481.71   $1,481.70   $1,481.70