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 $7.91   5.445%   $8.3407   $8.34   $8.35   $8.30  
  Purchase #2 $161.48   7.125%   $172.9855   $172.99   $173.00   $173.00  
  Purchase #3 $109.86   3.755%   $113.9852   $113.99   $114.00   $114.00  
  Purchase #4 $125.56   7.694%   $135.2206   $135.22   $135.20   $135.20  
  Purchase #5 $29.44   12.530%   $33.1288   $33.13   $33.15   $33.10  
  Purchase #6 $43.73   10.591%   $48.3614   $48.36   $48.35   $48.40  
  Purchase #7 $53.52   7.775%   $57.6812   $57.68   $57.70   $57.70  
  7 purchase totals = $531.50       $569.7034   $569.71   $569.75   $569.70