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 $179.49   10.353%   $198.0726   $198.07   $198.05   $198.10  
  Purchase #2 $242.97   10.156%   $267.646   $267.65   $267.65   $267.60  
  Purchase #3 $87.92   3.503%   $90.9998   $91.00   $91.00   $91.00  
  Purchase #4 $139.25   12.633%   $156.8415   $156.84   $156.85   $156.80  
  Purchase #5 $69.74   8.674%   $75.7892   $75.79   $75.80   $75.80  
  Purchase #6 $26.31   7.401%   $28.2572   $28.26   $28.25   $28.30  
  Purchase #7 $93.62   6.308%   $99.5255   $99.53   $99.55   $99.50  
  7 purchase totals = $839.30       $917.1318   $917.14   $917.15   $917.10