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 $212.60   6.547%   $226.5189   $226.52   $226.50   $226.50  
  Purchase #2 $55.59   5.789%   $58.8081   $58.81   $58.80   $58.80  
  Purchase #3 $244.38   8.643%   $265.5018   $265.50   $265.50   $265.50  
  Purchase #4 $43.74   6.565%   $46.6115   $46.61   $46.60   $46.60  
  Purchase #5 $247.54   12.537%   $278.5741   $278.57   $278.55   $278.60  
  Purchase #6 $202.85   11.629%   $226.4394   $226.44   $226.45   $226.40  
  Purchase #7 $39.25   9.708%   $43.0604   $43.06   $43.05   $43.10  
  7 purchase totals = $1,045.95       $1,145.5142   $1,145.51   $1,145.45   $1,145.50