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 $241.33   12.576%   $271.6797   $271.68   $271.70   $271.70  
  Purchase #2 $106.95   4.699%   $111.9756   $111.98   $112.00   $112.00  
  Purchase #3 $84.84   4.612%   $88.7528   $88.75   $88.75   $88.80  
  Purchase #4 $163.97   10.758%   $181.6099   $181.61   $181.60   $181.60  
  Purchase #5 $226.31   11.726%   $252.8471   $252.85   $252.85   $252.80  
  Purchase #6 $233.79   12.748%   $263.5935   $263.59   $263.60   $263.60  
  Purchase #7 $238.73   11.444%   $266.0503   $266.05   $266.05   $266.10  
  7 purchase totals = $1,295.92       $1,436.5089   $1,436.51   $1,436.55   $1,436.60