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 $10.46   8.557%   $11.3551   $11.36   $11.35   $11.40  
  Purchase #2 $103.95   10.299%   $114.6558   $114.66   $114.65   $114.70  
  Purchase #3 $107.37   6.682%   $114.5445   $114.54   $114.55   $114.50  
  Purchase #4 $149.98   8.867%   $163.2787   $163.28   $163.30   $163.30  
  Purchase #5 $163.59   11.217%   $181.9399   $181.94   $181.95   $181.90  
  Purchase #6 $224.38   4.840%   $235.24   $235.24   $235.25   $235.20  
  Purchase #7 $192.29   4.159%   $200.2873   $200.29   $200.30   $200.30  
  7 purchase totals = $952.02       $1,021.3013   $1,021.31   $1,021.35   $1,021.30