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 $62.88   9.748%   $69.0095   $69.01   $69.00   $69.00  
  Purchase #2 $234.94   3.697%   $243.6257   $243.63   $243.65   $243.60  
  Purchase #3 $69.94   7.867%   $75.4422   $75.44   $75.45   $75.40  
  Purchase #4 $72.56   9.470%   $79.4314   $79.43   $79.45   $79.40  
  Purchase #5 $182.84   9.244%   $199.7417   $199.74   $199.75   $199.70  
  Purchase #6 $197.63   9.715%   $216.8298   $216.83   $216.85   $216.80  
  Purchase #7 $126.27   13.874%   $143.7887   $143.79   $143.80   $143.80  
  7 purchase totals = $947.06       $1,027.8690   $1,027.87   $1,027.95   $1,027.70