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 $195.50   4.291%   $203.8889   $203.89   $203.90   $203.90  
  Purchase #2 $24.65   4.239%   $25.6949   $25.69   $25.70   $25.70  
  Purchase #3 $51.56   5.508%   $54.3999   $54.40   $54.40   $54.40  
  Purchase #4 $244.63   8.300%   $264.9343   $264.93   $264.95   $264.90  
  Purchase #5 $186.66   13.666%   $212.169   $212.17   $212.15   $212.20  
  Purchase #6 $68.69   7.728%   $73.9984   $74.00   $74.00   $74.00  
  Purchase #7 $179.66   6.317%   $191.0091   $191.01   $191.00   $191.00  
  7 purchase totals = $951.35       $1,026.0945   $1,026.09   $1,026.10   $1,026.10