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 $139.52   7.247%   $149.631   $149.63   $149.65   $149.60  
  Purchase #2 $61.47   7.229%   $65.9137   $65.91   $65.90   $65.90  
  Purchase #3 $168.36   6.405%   $179.1435   $179.14   $179.15   $179.10  
  Purchase #4 $244.49   8.657%   $265.6555   $265.66   $265.65   $265.70  
  Purchase #5 $5.33   4.409%   $5.565   $5.57   $5.55   $5.60  
  Purchase #6 $240.82   5.436%   $253.911   $253.91   $253.90   $253.90  
  Purchase #7 $224.66   4.155%   $233.9946   $233.99   $234.00   $234.00  
  7 purchase totals = $1,084.65       $1,153.8143   $1,153.81   $1,153.80   $1,153.80