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 $188.66   4.257%   $196.6913   $196.69   $196.70   $196.70  
  Purchase #2 $95.68   11.310%   $106.5014   $106.50   $106.50   $106.50  
  Purchase #3 $87.88   3.794%   $91.2142   $91.21   $91.20   $91.20  
  Purchase #4 $228.92   8.286%   $247.8883   $247.89   $247.90   $247.90  
  Purchase #5 $35.77   5.277%   $37.6576   $37.66   $37.65   $37.70  
  Purchase #6 $57.26   12.141%   $64.2119   $64.21   $64.20   $64.20  
  Purchase #7 $59.55   3.857%   $61.8468   $61.85   $61.85   $61.80  
  7 purchase totals = $753.72       $806.0115   $806.01   $806.00   $806.00