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 $65.44   13.564%   $74.3163   $74.32   $74.30   $74.30  
  Purchase #2 $86.95   12.777%   $98.0596   $98.06   $98.05   $98.10  
  Purchase #3 $193.94   6.519%   $206.5829   $206.58   $206.60   $206.60  
  Purchase #4 $182.89   11.737%   $204.3558   $204.36   $204.35   $204.40  
  Purchase #5 $118.79   4.645%   $124.3078   $124.31   $124.30   $124.30  
  Purchase #6 $148.43   6.170%   $157.5881   $157.59   $157.60   $157.60  
  Purchase #7 $212.59   8.174%   $229.9671   $229.97   $229.95   $230.00  
  7 purchase totals = $1,009.03       $1,095.1776   $1,095.19   $1,095.15   $1,095.30