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 $59.82   13.612%   $67.9627   $67.96   $67.95   $68.00  
  Purchase #2 $135.62   12.414%   $152.4559   $152.46   $152.45   $152.50  
  Purchase #3 $235.55   5.378%   $248.2179   $248.22   $248.20   $248.20  
  Purchase #4 $140.84   7.293%   $151.1115   $151.11   $151.10   $151.10  
  Purchase #5 $227.70   3.452%   $235.5602   $235.56   $235.55   $235.60  
  Purchase #6 $213.90   7.636%   $230.2334   $230.23   $230.25   $230.20  
  Purchase #7 $83.52   6.457%   $88.9129   $88.91   $88.90   $88.90  
  7 purchase totals = $1,096.95       $1,174.4545   $1,174.45   $1,174.40   $1,174.50