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 $65.88   13.628%   $74.8581   $74.86   $74.85   $74.90  
  Purchase #2 $57.89   9.853%   $63.5939   $63.59   $63.60   $63.60  
  Purchase #3 $70.93   12.162%   $79.5565   $79.56   $79.55   $79.60  
  Purchase #4 $222.65   8.729%   $242.0851   $242.09   $242.10   $242.10  
  Purchase #5 $92.47   6.125%   $98.1338   $98.13   $98.15   $98.10  
  Purchase #6 $219.28   6.257%   $233.0003   $233.00   $233.00   $233.00  
  Purchase #7 $8.61   5.772%   $9.107   $9.11   $9.10   $9.10  
  7 purchase totals = $737.71       $800.3347   $800.34   $800.35   $800.40