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 $187.93   8.470%   $203.8477   $203.85   $203.85   $203.80  
  Purchase #2 $215.66   7.165%   $231.112   $231.11   $231.10   $231.10  
  Purchase #3 $243.92   13.342%   $276.4638   $276.46   $276.45   $276.50  
  Purchase #4 $189.64   13.542%   $215.321   $215.32   $215.30   $215.30  
  Purchase #5 $67.32   8.800%   $73.2442   $73.24   $73.25   $73.20  
  Purchase #6 $181.39   9.150%   $197.9872   $197.99   $198.00   $198.00  
  Purchase #7 $86.92   9.474%   $95.1548   $95.15   $95.15   $95.20  
  7 purchase totals = $1,172.78       $1,293.1307   $1,293.12   $1,293.10   $1,293.10