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 $70.49   4.391%   $73.5852   $73.59   $73.60   $73.60  
  Purchase #2 $49.35   11.695%   $55.1215   $55.12   $55.10   $55.10  
  Purchase #3 $68.35   4.162%   $71.1947   $71.19   $71.20   $71.20  
  Purchase #4 $229.96   8.218%   $248.8581   $248.86   $248.85   $248.90  
  Purchase #5 $119.49   13.791%   $135.9689   $135.97   $135.95   $136.00  
  Purchase #6 $165.47   9.394%   $181.0143   $181.01   $181.00   $181.00  
  Purchase #7 $80.75   12.627%   $90.9463   $90.95   $90.95   $90.90  
  7 purchase totals = $783.86       $856.6890   $856.69   $856.65   $856.70