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 $176.91   9.210%   $193.2034   $193.20   $193.20   $193.20  
  Purchase #2 $7.59   5.351%   $7.9961   $8.00   $8.00   $8.00  
  Purchase #3 $146.76   12.754%   $165.4778   $165.48   $165.50   $165.50  
  Purchase #4 $41.47   7.234%   $44.4699   $44.47   $44.45   $44.50  
  Purchase #5 $226.45   6.410%   $240.9654   $240.97   $240.95   $241.00  
  Purchase #6 $51.46   12.422%   $57.8524   $57.85   $57.85   $57.90  
  Purchase #7 $119.32   11.755%   $133.3461   $133.35   $133.35   $133.30  
  7 purchase totals = $769.96       $843.3111   $843.32   $843.30   $843.40