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 $182.52   7.574%   $196.3441   $196.34   $196.35   $196.30  
  Purchase #2 $116.62   6.395%   $124.0778   $124.08   $124.10   $124.10  
  Purchase #3 $209.59   6.727%   $223.6891   $223.69   $223.70   $223.70  
  Purchase #4 $155.59   7.489%   $167.2421   $167.24   $167.25   $167.20  
  Purchase #5 $247.60   9.621%   $271.4216   $271.42   $271.40   $271.40  
  Purchase #6 $13.26   11.257%   $14.7527   $14.75   $14.75   $14.80  
  Purchase #7 $229.43   8.652%   $249.2803   $249.28   $249.30   $249.30  
  7 purchase totals = $1,154.61       $1,246.8077   $1,246.80   $1,246.85   $1,246.80