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 $218.32   8.293%   $236.4253   $236.43   $236.45   $236.40  
  Purchase #2 $50.54   13.141%   $57.1815   $57.18   $57.20   $57.20  
  Purchase #3 $235.28   3.588%   $243.7218   $243.72   $243.70   $243.70  
  Purchase #4 $116.81   8.121%   $126.2961   $126.30   $126.30   $126.30  
  Purchase #5 $44.79   8.614%   $48.6482   $48.65   $48.65   $48.60  
  Purchase #6 $85.70   9.488%   $93.8312   $93.83   $93.85   $93.80  
  Purchase #7 $202.51   7.392%   $217.4795   $217.48   $217.50   $217.50  
  7 purchase totals = $953.95       $1,023.5836   $1,023.59   $1,023.65   $1,023.50