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 $170.65   8.403%   $184.9897   $184.99   $185.00   $185.00  
  Purchase #2 $224.59   6.629%   $239.4781   $239.48   $239.50   $239.50  
  Purchase #3 $24.48   3.248%   $25.2751   $25.28   $25.30   $25.30  
  Purchase #4 $219.72   7.426%   $236.0364   $236.04   $236.05   $236.00  
  Purchase #5 $149.83   11.241%   $166.6724   $166.67   $166.65   $166.70  
  Purchase #6 $31.65   5.488%   $33.387   $33.39   $33.40   $33.40  
  Purchase #7 $210.82   4.412%   $220.1214   $220.12   $220.10   $220.10  
  7 purchase totals = $1,031.74       $1,105.9601   $1,105.97   $1,106.00   $1,106.00