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 $87.94   6.357%   $93.5303   $93.53   $93.55   $93.50  
  Purchase #2 $229.51   5.512%   $242.1606   $242.16   $242.15   $242.20  
  Purchase #3 $127.48   8.221%   $137.9601   $137.96   $137.95   $138.00  
  Purchase #4 $248.87   5.471%   $262.4857   $262.49   $262.50   $262.50  
  Purchase #5 $53.25   6.773%   $56.8566   $56.86   $56.85   $56.90  
  Purchase #6 $98.47   4.716%   $103.1138   $103.11   $103.10   $103.10  
  Purchase #7 $94.72   11.581%   $105.6895   $105.69   $105.70   $105.70  
  7 purchase totals = $940.24       $1,001.7966   $1,001.80   $1,001.80   $1,001.90