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 $23.47   10.277%   $25.882   $25.88   $25.90   $25.90  
  Purchase #2 $192.90   7.624%   $207.6067   $207.61   $207.60   $207.60  
  Purchase #3 $97.26   4.709%   $101.84   $101.84   $101.85   $101.80  
  Purchase #4 $10.76   8.216%   $11.644   $11.64   $11.65   $11.60  
  Purchase #5 $31.29   8.798%   $34.0429   $34.04   $34.05   $34.00  
  Purchase #6 $11.92   13.361%   $13.5126   $13.51   $13.50   $13.50  
  Purchase #7 $90.52   10.253%   $99.801   $99.80   $99.80   $99.80  
  7 purchase totals = $458.12       $494.3292   $494.32   $494.35   $494.20