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 $41.33   4.159%   $43.0489   $43.05   $43.05   $43.00  
  Purchase #2 $192.93   7.518%   $207.4345   $207.43   $207.45   $207.40  
  Purchase #3 $88.93   6.375%   $94.5993   $94.60   $94.60   $94.60  
  Purchase #4 $206.83   9.137%   $225.7281   $225.73   $225.75   $225.70  
  Purchase #5 $185.85   6.463%   $197.8615   $197.86   $197.85   $197.90  
  Purchase #6 $89.93   12.393%   $101.075   $101.08   $101.10   $101.10  
  Purchase #7 $84.43   8.466%   $91.5778   $91.58   $91.60   $91.60  
  7 purchase totals = $890.23       $961.3251   $961.33   $961.40   $961.30