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 $181.99   8.772%   $197.9542   $197.95   $197.95   $198.00  
  Purchase #2 $6.59   13.860%   $7.5034   $7.50   $7.50   $7.50  
  Purchase #3 $122.97   13.569%   $139.6558   $139.66   $139.65   $139.70  
  Purchase #4 $62.77   8.478%   $68.0916   $68.09   $68.10   $68.10  
  Purchase #5 $174.68   12.678%   $196.8259   $196.83   $196.85   $196.80  
  Purchase #6 $72.76   5.301%   $76.617   $76.62   $76.60   $76.60  
  Purchase #7 $61.43   4.200%   $64.0101   $64.01   $64.00   $64.00  
  7 purchase totals = $683.19       $750.6580   $750.66   $750.65   $750.70