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 $223.36   6.761%   $238.4614   $238.46   $238.45   $238.50  
  Purchase #2 $127.87   11.754%   $142.8998   $142.90   $142.90   $142.90  
  Purchase #3 $215.26   8.404%   $233.3505   $233.35   $233.35   $233.40  
  Purchase #4 $115.92   8.333%   $125.5796   $125.58   $125.60   $125.60  
  Purchase #5 $128.38   11.668%   $143.3594   $143.36   $143.35   $143.40  
  Purchase #6 $125.35   3.681%   $129.9641   $129.96   $129.95   $130.00  
  Purchase #7 $11.97   11.114%   $13.3003   $13.30   $13.30   $13.30  
  7 purchase totals = $948.11       $1,026.9151   $1,026.91   $1,026.90   $1,027.10