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 $23.58   10.257%   $25.9986   $26.00   $26.00   $26.00  
  Purchase #2 $74.72   11.482%   $83.2994   $83.30   $83.30   $83.30  
  Purchase #3 $189.87   6.146%   $201.5394   $201.54   $201.55   $201.50  
  Purchase #4 $130.35   13.185%   $147.5366   $147.54   $147.55   $147.50  
  Purchase #5 $119.37   9.555%   $130.7758   $130.78   $130.80   $130.80  
  Purchase #6 $16.55   13.563%   $18.7947   $18.79   $18.80   $18.80  
  Purchase #7 $89.83   5.763%   $95.0069   $95.01   $95.00   $95.00  
  7 purchase totals = $644.27       $702.9514   $702.96   $703.00   $702.90