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 $176.77   5.708%   $186.86   $186.86   $186.85   $186.90  
  Purchase #2 $152.72   6.835%   $163.1584   $163.16   $163.15   $163.20  
  Purchase #3 $162.30   6.665%   $173.1173   $173.12   $173.10   $173.10  
  Purchase #4 $211.55   3.593%   $219.151   $219.15   $219.15   $219.20  
  Purchase #5 $84.57   9.180%   $92.3335   $92.33   $92.35   $92.30  
  Purchase #6 $224.93   9.387%   $246.0442   $246.04   $246.05   $246.00  
  Purchase #7 $185.45   4.591%   $193.964   $193.96   $193.95   $194.00  
  7 purchase totals = $1,198.29       $1,274.6284   $1,274.62   $1,274.60   $1,274.70