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 $83.87   12.310%   $94.1944   $94.19   $94.20   $94.20  
  Purchase #2 $148.41   11.584%   $165.6018   $165.60   $165.60   $165.60  
  Purchase #3 $137.42   5.532%   $145.0221   $145.02   $145.00   $145.00  
  Purchase #4 $100.89   13.798%   $114.8108   $114.81   $114.80   $114.80  
  Purchase #5 $199.87   4.561%   $208.9861   $208.99   $209.00   $209.00  
  Purchase #6 $94.55   10.228%   $104.2206   $104.22   $104.20   $104.20  
  Purchase #7 $246.34   8.403%   $267.04   $267.04   $267.05   $267.00  
  7 purchase totals = $1,011.35       $1,099.8758   $1,099.87   $1,099.85   $1,099.80