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 $118.92   6.441%   $126.5796   $126.58   $126.60   $126.60  
  Purchase #2 $133.36   6.740%   $142.3485   $142.35   $142.35   $142.30  
  Purchase #3 $16.87   3.450%   $17.452   $17.45   $17.45   $17.50  
  Purchase #4 $188.76   12.164%   $211.7208   $211.72   $211.70   $211.70  
  Purchase #5 $137.56   5.250%   $144.7819   $144.78   $144.80   $144.80  
  Purchase #6 $161.95   8.430%   $175.6024   $175.60   $175.60   $175.60  
  Purchase #7 $216.74   5.656%   $228.9988   $229.00   $229.00   $229.00  
  7 purchase totals = $974.16       $1,047.4840   $1,047.48   $1,047.50   $1,047.50