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 $206.93   9.515%   $226.6194   $226.62   $226.60   $226.60  
  Purchase #2 $132.72   11.221%   $147.6125   $147.61   $147.60   $147.60  
  Purchase #3 $110.98   6.179%   $117.8375   $117.84   $117.85   $117.80  
  Purchase #4 $135.34   9.845%   $148.6642   $148.66   $148.65   $148.70  
  Purchase #5 $232.76   5.297%   $245.0893   $245.09   $245.10   $245.10  
  Purchase #6 $17.48   8.763%   $19.0118   $19.01   $19.00   $19.00  
  Purchase #7 $233.45   9.338%   $255.2496   $255.25   $255.25   $255.20  
  7 purchase totals = $1,069.66       $1,160.0843   $1,160.08   $1,160.05   $1,160.00