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 $108.32   9.464%   $118.5714   $118.57   $118.55   $118.60  
  Purchase #2 $155.52   3.685%   $161.2509   $161.25   $161.25   $161.30  
  Purchase #3 $203.60   7.487%   $218.8435   $218.84   $218.85   $218.80  
  Purchase #4 $52.46   10.846%   $58.1498   $58.15   $58.15   $58.10  
  Purchase #5 $212.59   5.579%   $224.4504   $224.45   $224.45   $224.50  
  Purchase #6 $195.52   7.663%   $210.5027   $210.50   $210.50   $210.50  
  Purchase #7 $37.75   13.130%   $42.7066   $42.71   $42.70   $42.70  
  7 purchase totals = $965.76       $1,034.4753   $1,034.47   $1,034.45   $1,034.50