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 $215.64   6.768%   $230.2345   $230.23   $230.25   $230.20  
  Purchase #2 $135.90   8.638%   $147.639   $147.64   $147.65   $147.60  
  Purchase #3 $231.48   9.442%   $253.3363   $253.34   $253.35   $253.30  
  Purchase #4 $8.32   9.507%   $9.111   $9.11   $9.10   $9.10  
  Purchase #5 $44.98   10.814%   $49.8441   $49.84   $49.85   $49.80  
  Purchase #6 $149.55   11.560%   $166.838   $166.84   $166.85   $166.80  
  Purchase #7 $70.85   12.483%   $79.6942   $79.69   $79.70   $79.70  
  7 purchase totals = $856.72       $936.6971   $936.69   $936.75   $936.50