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 $62.64   12.201%   $70.2827   $70.28   $70.30   $70.30  
  Purchase #2 $104.41   8.372%   $113.1512   $113.15   $113.15   $113.20  
  Purchase #3 $247.53   6.423%   $263.4289   $263.43   $263.45   $263.40  
  Purchase #4 $90.79   12.201%   $101.8673   $101.87   $101.85   $101.90  
  Purchase #5 $229.29   4.601%   $239.8396   $239.84   $239.85   $239.80  
  Purchase #6 $215.29   8.609%   $233.8243   $233.82   $233.80   $233.80  
  Purchase #7 $179.93   6.295%   $191.2566   $191.26   $191.25   $191.30  
  7 purchase totals = $1,129.88       $1,213.6506   $1,213.65   $1,213.65   $1,213.70