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 $55.80   12.619%   $62.8414   $62.84   $62.85   $62.80  
  Purchase #2 $60.40   7.343%   $64.8352   $64.84   $64.85   $64.80  
  Purchase #3 $115.66   6.339%   $122.9917   $122.99   $123.00   $123.00  
  Purchase #4 $245.87   5.514%   $259.4273   $259.43   $259.45   $259.40  
  Purchase #5 $167.87   10.691%   $185.817   $185.82   $185.80   $185.80  
  Purchase #6 $110.36   11.402%   $122.9432   $122.94   $122.95   $122.90  
  Purchase #7 $98.66   8.791%   $107.3332   $107.33   $107.35   $107.30  
  7 purchase totals = $854.62       $926.1890   $926.19   $926.25   $926.00