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 $96.92   6.558%   $103.276   $103.28   $103.30   $103.30  
  Purchase #2 $129.43   13.460%   $146.8513   $146.85   $146.85   $146.90  
  Purchase #3 $96.83   5.504%   $102.1595   $102.16   $102.15   $102.20  
  Purchase #4 $14.32   11.543%   $15.973   $15.97   $15.95   $16.00  
  Purchase #5 $97.84   11.221%   $108.8186   $108.82   $108.80   $108.80  
  Purchase #6 $211.99   10.835%   $234.9591   $234.96   $234.95   $235.00  
  Purchase #7 $106.92   7.257%   $114.6792   $114.68   $114.70   $114.70  
  7 purchase totals = $754.25       $826.7167   $826.72   $826.70   $826.90