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 $58.66   4.127%   $61.0809   $61.08   $61.10   $61.10  
  Purchase #2 $206.66   8.145%   $223.4925   $223.49   $223.50   $223.50  
  Purchase #3 $15.99   3.221%   $16.505   $16.51   $16.50   $16.50  
  Purchase #4 $127.68   3.812%   $132.5472   $132.55   $132.55   $132.50  
  Purchase #5 $125.86   3.178%   $129.8598   $129.86   $129.85   $129.90  
  Purchase #6 $147.41   7.295%   $158.1636   $158.16   $158.15   $158.20  
  Purchase #7 $198.98   3.203%   $205.3533   $205.35   $205.35   $205.40  
  7 purchase totals = $881.24       $927.0023   $927.00   $927.00   $927.10