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 $60.95   9.197%   $66.5556   $66.56   $66.55   $66.60  
  Purchase #2 $227.50   7.129%   $243.7185   $243.72   $243.70   $243.70  
  Purchase #3 $57.95   12.825%   $65.3821   $65.38   $65.40   $65.40  
  Purchase #4 $218.29   13.485%   $247.7264   $247.73   $247.75   $247.70  
  Purchase #5 $75.61   6.788%   $80.7424   $80.74   $80.75   $80.70  
  Purchase #6 $154.34   7.468%   $165.8661   $165.87   $165.85   $165.90  
  Purchase #7 $225.55   8.788%   $245.3713   $245.37   $245.35   $245.40  
  7 purchase totals = $1,020.19       $1,115.3624   $1,115.37   $1,115.35   $1,115.40