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 $165.54   8.118%   $178.9785   $178.98   $179.00   $179.00  
  Purchase #2 $190.69   4.331%   $198.9488   $198.95   $198.95   $198.90  
  Purchase #3 $178.33   8.325%   $193.176   $193.18   $193.20   $193.20  
  Purchase #4 $135.88   6.164%   $144.2556   $144.26   $144.25   $144.30  
  Purchase #5 $51.51   3.179%   $53.1475   $53.15   $53.15   $53.10  
  Purchase #6 $177.92   9.165%   $194.2264   $194.23   $194.25   $194.20  
  Purchase #7 $63.35   9.797%   $69.5564   $69.56   $69.55   $69.60  
  7 purchase totals = $963.22       $1,032.2892   $1,032.31   $1,032.35   $1,032.30