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 $138.49   12.567%   $155.894   $155.89   $155.90   $155.90  
  Purchase #2 $77.80   9.437%   $85.142   $85.14   $85.15   $85.10  
  Purchase #3 $95.64   7.627%   $102.9345   $102.93   $102.95   $102.90  
  Purchase #4 $224.98   6.696%   $240.0447   $240.04   $240.05   $240.00  
  Purchase #5 $221.92   4.539%   $231.9929   $231.99   $232.00   $232.00  
  Purchase #6 $245.34   8.379%   $265.897   $265.90   $265.90   $265.90  
  Purchase #7 $80.72   6.685%   $86.1161   $86.12   $86.10   $86.10  
  7 purchase totals = $1,084.89       $1,168.0212   $1,168.01   $1,168.05   $1,167.90