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 $71.25   3.284%   $73.5899   $73.59   $73.60   $73.60  
  Purchase #2 $41.77   13.528%   $47.4206   $47.42   $47.40   $47.40  
  Purchase #3 $168.88   12.694%   $190.3176   $190.32   $190.30   $190.30  
  Purchase #4 $225.52   12.518%   $253.7506   $253.75   $253.75   $253.80  
  Purchase #5 $165.49   9.684%   $181.5161   $181.52   $181.50   $181.50  
  Purchase #6 $23.40   13.310%   $26.5145   $26.51   $26.50   $26.50  
  Purchase #7 $8.43   12.435%   $9.4783   $9.48   $9.50   $9.50  
  7 purchase totals = $704.74       $782.5876   $782.59   $782.55   $782.60