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 $216.88   13.705%   $246.6034   $246.60   $246.60   $246.60  
  Purchase #2 $61.66   12.608%   $69.4341   $69.43   $69.45   $69.40  
  Purchase #3 $86.76   9.506%   $95.0074   $95.01   $95.00   $95.00  
  Purchase #4 $198.55   11.588%   $221.558   $221.56   $221.55   $221.60  
  Purchase #5 $164.27   3.343%   $169.7615   $169.76   $169.75   $169.80  
  Purchase #6 $79.44   7.662%   $85.5267   $85.53   $85.55   $85.50  
  Purchase #7 $163.46   4.765%   $171.2489   $171.25   $171.25   $171.20  
  7 purchase totals = $971.02       $1,059.1400   $1,059.14   $1,059.15   $1,059.10