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 $198.38   6.158%   $210.5962   $210.60   $210.60   $210.60  
  Purchase #2 $85.59   9.654%   $93.8529   $93.85   $93.85   $93.90  
  Purchase #3 $216.97   13.422%   $246.0917   $246.09   $246.10   $246.10  
  Purchase #4 $239.99   6.223%   $254.9246   $254.92   $254.90   $254.90  
  Purchase #5 $66.90   13.311%   $75.8051   $75.81   $75.80   $75.80  
  Purchase #6 $46.39   13.412%   $52.6118   $52.61   $52.60   $52.60  
  Purchase #7 $227.71   3.494%   $235.6662   $235.67   $235.65   $235.70  
  7 purchase totals = $1,081.93       $1,169.5485   $1,169.55   $1,169.50   $1,169.60