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 $111.45   13.309%   $126.2829   $126.28   $126.30   $126.30  
  Purchase #2 $222.96   10.482%   $246.3307   $246.33   $246.35   $246.30  
  Purchase #3 $72.43   11.356%   $80.6552   $80.66   $80.65   $80.70  
  Purchase #4 $181.52   8.688%   $197.2905   $197.29   $197.30   $197.30  
  Purchase #5 $230.41   7.489%   $247.6654   $247.67   $247.65   $247.70  
  Purchase #6 $129.41   13.227%   $146.5271   $146.53   $146.55   $146.50  
  Purchase #7 $160.67   11.332%   $178.8771   $178.88   $178.90   $178.90  
  7 purchase totals = $1,108.85       $1,223.6289   $1,223.64   $1,223.70   $1,223.70