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 $166.93   12.656%   $188.0567   $188.06   $188.05   $188.10  
  Purchase #2 $154.92   8.359%   $167.8698   $167.87   $167.85   $167.90  
  Purchase #3 $23.62   8.741%   $25.6846   $25.68   $25.70   $25.70  
  Purchase #4 $52.66   7.123%   $56.411   $56.41   $56.40   $56.40  
  Purchase #5 $138.75   8.633%   $150.7283   $150.73   $150.75   $150.70  
  Purchase #6 $228.47   5.395%   $240.796   $240.80   $240.80   $240.80  
  Purchase #7 $189.88   3.399%   $196.334   $196.33   $196.35   $196.30  
  7 purchase totals = $955.23       $1,025.8804   $1,025.88   $1,025.90   $1,025.90