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 $163.91   13.207%   $185.5576   $185.56   $185.55   $185.60  
  Purchase #2 $48.35   12.653%   $54.4677   $54.47   $54.45   $54.50  
  Purchase #3 $87.42   8.524%   $94.8717   $94.87   $94.85   $94.90  
  Purchase #4 $173.63   10.572%   $191.9862   $191.99   $192.00   $192.00  
  Purchase #5 $176.78   11.399%   $196.9312   $196.93   $196.95   $196.90  
  Purchase #6 $206.91   6.495%   $220.3488   $220.35   $220.35   $220.30  
  Purchase #7 $247.84   11.156%   $275.489   $275.49   $275.50   $275.50  
  7 purchase totals = $1,104.84       $1,219.6522   $1,219.66   $1,219.65   $1,219.70