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 $88.87   10.192%   $97.9276   $97.93   $97.95   $97.90  
  Purchase #2 $13.36   7.557%   $14.3696   $14.37   $14.35   $14.40  
  Purchase #3 $211.47   10.374%   $233.4079   $233.41   $233.40   $233.40  
  Purchase #4 $72.87   11.371%   $81.156   $81.16   $81.15   $81.20  
  Purchase #5 $50.47   8.641%   $54.8311   $54.83   $54.85   $54.80  
  Purchase #6 $196.87   4.486%   $205.7016   $205.70   $205.70   $205.70  
  Purchase #7 $204.69   8.223%   $221.5217   $221.52   $221.50   $221.50  
  7 purchase totals = $838.60       $908.9155   $908.92   $908.90   $908.90