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 $38.77   6.406%   $41.2536   $41.25   $41.25   $41.30  
  Purchase #2 $52.46   12.187%   $58.8533   $58.85   $58.85   $58.90  
  Purchase #3 $179.63   13.529%   $203.9321   $203.93   $203.95   $203.90  
  Purchase #4 $190.45   8.691%   $207.002   $207.00   $207.00   $207.00  
  Purchase #5 $76.79   10.716%   $85.0188   $85.02   $85.00   $85.00  
  Purchase #6 $168.46   10.600%   $186.3168   $186.32   $186.30   $186.30  
  Purchase #7 $247.41   5.114%   $260.0625   $260.06   $260.05   $260.10  
  7 purchase totals = $953.97       $1,042.4391   $1,042.43   $1,042.40   $1,042.50