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 $54.86   12.524%   $61.7307   $61.73   $61.75   $61.70  
  Purchase #2 $181.86   11.263%   $202.3429   $202.34   $202.35   $202.30  
  Purchase #3 $43.83   5.422%   $46.2065   $46.21   $46.20   $46.20  
  Purchase #4 $7.88   11.670%   $8.7996   $8.80   $8.80   $8.80  
  Purchase #5 $132.51   4.217%   $138.0979   $138.10   $138.10   $138.10  
  Purchase #6 $156.59   10.460%   $172.9693   $172.97   $172.95   $173.00  
  Purchase #7 $168.58   10.534%   $186.3382   $186.34   $186.35   $186.30  
  7 purchase totals = $746.11       $816.4851   $816.49   $816.50   $816.40