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 $62.54   11.729%   $69.8753   $69.88   $69.90   $69.90  
  Purchase #2 $192.95   5.137%   $202.8618   $202.86   $202.85   $202.90  
  Purchase #3 $116.58   6.815%   $124.5249   $124.52   $124.50   $124.50  
  Purchase #4 $223.70   7.152%   $239.699   $239.70   $239.70   $239.70  
  Purchase #5 $227.35   5.113%   $238.9744   $238.97   $238.95   $239.00  
  Purchase #6 $209.35   9.445%   $229.1231   $229.12   $229.10   $229.10  
  Purchase #7 $115.35   10.510%   $127.4733   $127.47   $127.45   $127.50  
  7 purchase totals = $1,147.82       $1,232.5318   $1,232.52   $1,232.45   $1,232.60