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 $22.61   6.425%   $24.0627   $24.06   $24.05   $24.10  
  Purchase #2 $241.64   12.265%   $271.2771   $271.28   $271.30   $271.30  
  Purchase #3 $63.60   7.662%   $68.473   $68.47   $68.45   $68.50  
  Purchase #4 $133.29   13.839%   $151.736   $151.74   $151.75   $151.70  
  Purchase #5 $194.60   8.604%   $211.3434   $211.34   $211.35   $211.30  
  Purchase #6 $64.39   8.874%   $70.104   $70.10   $70.10   $70.10  
  Purchase #7 $191.73   12.755%   $216.1852   $216.19   $216.20   $216.20  
  7 purchase totals = $911.86       $1,013.1814   $1,013.18   $1,013.20   $1,013.20