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 $23.87   9.343%   $26.1002   $26.10   $26.10   $26.10  
  Purchase #2 $186.52   13.842%   $212.3381   $212.34   $212.35   $212.30  
  Purchase #3 $233.51   9.158%   $254.8948   $254.89   $254.90   $254.90  
  Purchase #4 $137.53   3.829%   $142.796   $142.80   $142.80   $142.80  
  Purchase #5 $69.97   10.230%   $77.1279   $77.13   $77.15   $77.10  
  Purchase #6 $184.26   12.630%   $207.532   $207.53   $207.55   $207.50  
  Purchase #7 $62.89   7.278%   $67.4671   $67.47   $67.45   $67.50  
  7 purchase totals = $898.55       $988.2561   $988.26   $988.30   $988.20