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 $215.90   8.716%   $234.7178   $234.72   $234.70   $234.70  
  Purchase #2 $86.63   6.594%   $92.3424   $92.34   $92.35   $92.30  
  Purchase #3 $87.44   10.415%   $96.5469   $96.55   $96.55   $96.50  
  Purchase #4 $250.44   5.734%   $264.8002   $264.80   $264.80   $264.80  
  Purchase #5 $31.58   12.379%   $35.4893   $35.49   $35.50   $35.50  
  Purchase #6 $27.37   12.504%   $30.7923   $30.79   $30.80   $30.80  
  Purchase #7 $250.89   3.416%   $259.4604   $259.46   $259.45   $259.50  
  7 purchase totals = $950.25       $1,014.1493   $1,014.15   $1,014.15   $1,014.10