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 $217.39   11.188%   $241.7116   $241.71   $241.70   $241.70  
  Purchase #2 $52.74   6.602%   $56.2219   $56.22   $56.20   $56.20  
  Purchase #3 $142.88   9.766%   $156.8337   $156.83   $156.85   $156.80  
  Purchase #4 $209.62   9.117%   $228.7311   $228.73   $228.75   $228.70  
  Purchase #5 $246.49   12.734%   $277.878   $277.88   $277.90   $277.90  
  Purchase #6 $49.53   5.280%   $52.1452   $52.15   $52.15   $52.10  
  Purchase #7 $217.54   13.600%   $247.1254   $247.13   $247.15   $247.10  
  7 purchase totals = $1,136.19       $1,260.6469   $1,260.65   $1,260.70   $1,260.50