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 $75.93   8.727%   $82.5564   $82.56   $82.55   $82.60  
  Purchase #2 $178.27   4.862%   $186.9375   $186.94   $186.95   $186.90  
  Purchase #3 $176.88   10.126%   $194.7909   $194.79   $194.80   $194.80  
  Purchase #4 $113.72   11.119%   $126.3645   $126.36   $126.35   $126.40  
  Purchase #5 $73.87   8.316%   $80.013   $80.01   $80.00   $80.00  
  Purchase #6 $218.58   7.133%   $234.1713   $234.17   $234.15   $234.20  
  Purchase #7 $132.45   12.509%   $149.0182   $149.02   $149.00   $149.00  
  7 purchase totals = $969.70       $1,053.8518   $1,053.85   $1,053.80   $1,053.90