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 $103.29   13.695%   $117.4356   $117.44   $117.45   $117.40  
  Purchase #2 $175.90   12.383%   $197.6817   $197.68   $197.70   $197.70  
  Purchase #3 $220.77   11.692%   $246.5824   $246.58   $246.60   $246.60  
  Purchase #4 $249.43   6.288%   $265.1142   $265.11   $265.10   $265.10  
  Purchase #5 $165.69   3.840%   $172.0525   $172.05   $172.05   $172.10  
  Purchase #6 $72.28   11.663%   $80.71   $80.71   $80.70   $80.70  
  Purchase #7 $218.90   7.713%   $235.7838   $235.78   $235.80   $235.80  
  7 purchase totals = $1,206.26       $1,315.3602   $1,315.35   $1,315.40   $1,315.40