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 $175.30   10.429%   $193.582   $193.58   $193.60   $193.60  
  Purchase #2 $50.36   5.709%   $53.2351   $53.24   $53.25   $53.20  
  Purchase #3 $119.32   3.731%   $123.7718   $123.77   $123.75   $123.80  
  Purchase #4 $131.85   5.441%   $139.024   $139.02   $139.00   $139.00  
  Purchase #5 $161.41   12.253%   $181.1876   $181.19   $181.20   $181.20  
  Purchase #6 $141.70   5.415%   $149.3731   $149.37   $149.35   $149.40  
  Purchase #7 $168.86   4.439%   $176.3557   $176.36   $176.35   $176.40  
  7 purchase totals = $948.80       $1,016.5293   $1,016.53   $1,016.50   $1,016.60