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 $176.51   8.622%   $191.7287   $191.73   $191.75   $191.70  
  Purchase #2 $206.64   9.566%   $226.4072   $226.41   $226.40   $226.40  
  Purchase #3 $191.65   12.710%   $216.0087   $216.01   $216.00   $216.00  
  Purchase #4 $238.78   12.689%   $269.0788   $269.08   $269.10   $269.10  
  Purchase #5 $125.26   8.452%   $135.847   $135.85   $135.85   $135.80  
  Purchase #6 $165.80   3.634%   $171.8252   $171.83   $171.85   $171.80  
  Purchase #7 $104.72   9.828%   $115.0119   $115.01   $115.00   $115.00  
  7 purchase totals = $1,209.36       $1,325.9075   $1,325.92   $1,325.95   $1,325.80