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 $82.56   10.874%   $91.5376   $91.54   $91.55   $91.50  
  Purchase #2 $245.54   12.116%   $275.2896   $275.29   $275.30   $275.30  
  Purchase #3 $135.79   9.419%   $148.5801   $148.58   $148.60   $148.60  
  Purchase #4 $220.75   8.607%   $239.75   $239.75   $239.75   $239.80  
  Purchase #5 $85.59   10.176%   $94.2996   $94.30   $94.30   $94.30  
  Purchase #6 $144.30   7.858%   $155.6391   $155.64   $155.65   $155.60  
  Purchase #7 $182.52   5.466%   $192.4965   $192.50   $192.50   $192.50  
  7 purchase totals = $1,097.05       $1,197.5925   $1,197.60   $1,197.65   $1,197.60