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 $156.67   3.583%   $162.2835   $162.28   $162.30   $162.30  
  Purchase #2 $184.41   9.531%   $201.9861   $201.99   $202.00   $202.00  
  Purchase #3 $7.82   9.492%   $8.5623   $8.56   $8.55   $8.60  
  Purchase #4 $159.88   8.264%   $173.0925   $173.09   $173.10   $173.10  
  Purchase #5 $141.40   12.813%   $159.5176   $159.52   $159.50   $159.50  
  Purchase #6 $216.25   3.770%   $224.4026   $224.40   $224.40   $224.40  
  Purchase #7 $88.75   8.567%   $96.3532   $96.35   $96.35   $96.40  
  7 purchase totals = $955.18       $1,026.1978   $1,026.19   $1,026.20   $1,026.30