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 $110.86   10.680%   $122.6998   $122.70   $122.70   $122.70  
  Purchase #2 $226.88   8.223%   $245.5363   $245.54   $245.55   $245.50  
  Purchase #3 $80.37   11.813%   $89.8641   $89.86   $89.85   $89.90  
  Purchase #4 $85.61   9.582%   $93.8132   $93.81   $93.80   $93.80  
  Purchase #5 $201.30   8.654%   $218.7205   $218.72   $218.70   $218.70  
  Purchase #6 $62.27   3.788%   $64.6288   $64.63   $64.65   $64.60  
  Purchase #7 $23.74   9.551%   $26.0074   $26.01   $26.00   $26.00  
  7 purchase totals = $791.03       $861.2701   $861.27   $861.25   $861.20