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 $79.81   9.709%   $87.5588   $87.56   $87.55   $87.60  
  Purchase #2 $203.58   4.354%   $212.4439   $212.44   $212.45   $212.40  
  Purchase #3 $24.50   3.709%   $25.4087   $25.41   $25.40   $25.40  
  Purchase #4 $33.33   12.150%   $37.3796   $37.38   $37.40   $37.40  
  Purchase #5 $179.88   6.555%   $191.6711   $191.67   $191.65   $191.70  
  Purchase #6 $82.72   7.471%   $88.9   $88.90   $88.90   $88.90  
  Purchase #7 $68.32   6.320%   $72.6378   $72.64   $72.65   $72.60  
  7 purchase totals = $672.14       $715.9999   $716.00   $716.00   $716.00