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 $111.98   13.278%   $126.8487   $126.85   $126.85   $126.80  
  Purchase #2 $74.53   9.693%   $81.7542   $81.75   $81.75   $81.80  
  Purchase #3 $136.70   5.674%   $144.4564   $144.46   $144.45   $144.50  
  Purchase #4 $61.58   10.233%   $67.8815   $67.88   $67.90   $67.90  
  Purchase #5 $212.29   5.662%   $224.3099   $224.31   $224.30   $224.30  
  Purchase #6 $238.94   5.663%   $252.4712   $252.47   $252.45   $252.50  
  Purchase #7 $23.47   11.573%   $26.1862   $26.19   $26.20   $26.20  
  7 purchase totals = $859.49       $923.9081   $923.91   $923.90   $924.00