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 $186.92   9.548%   $204.7671   $204.77   $204.75   $204.80  
  Purchase #2 $216.98   13.369%   $245.9881   $245.99   $246.00   $246.00  
  Purchase #3 $19.50   6.312%   $20.7308   $20.73   $20.75   $20.70  
  Purchase #4 $220.31   6.792%   $235.2735   $235.27   $235.25   $235.30  
  Purchase #5 $236.32   6.723%   $252.2078   $252.21   $252.20   $252.20  
  Purchase #6 $80.58   10.678%   $89.1843   $89.18   $89.20   $89.20  
  Purchase #7 $156.33   6.200%   $166.0225   $166.02   $166.00   $166.00  
  7 purchase totals = $1,116.94       $1,214.1741   $1,214.17   $1,214.15   $1,214.20