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 $111.49   12.384%   $125.2969   $125.30   $125.30   $125.30  
  Purchase #2 $73.86   5.120%   $77.6416   $77.64   $77.65   $77.60  
  Purchase #3 $84.43   7.307%   $90.5993   $90.60   $90.60   $90.60  
  Purchase #4 $211.43   9.277%   $231.0444   $231.04   $231.05   $231.00  
  Purchase #5 $40.74   9.323%   $44.5382   $44.54   $44.55   $44.50  
  Purchase #6 $196.81   10.612%   $217.6955   $217.70   $217.70   $217.70  
  Purchase #7 $87.34   4.402%   $91.1847   $91.18   $91.20   $91.20  
  7 purchase totals = $806.10       $878.0006   $878.00   $878.05   $877.90