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 $236.57   9.576%   $259.2239   $259.22   $259.20   $259.20  
  Purchase #2 $127.34   4.172%   $132.6526   $132.65   $132.65   $132.70  
  Purchase #3 $125.96   4.824%   $132.0363   $132.04   $132.05   $132.00  
  Purchase #4 $42.54   9.784%   $46.7021   $46.70   $46.70   $46.70  
  Purchase #5 $183.37   6.545%   $195.3716   $195.37   $195.35   $195.40  
  Purchase #6 $190.85   10.760%   $211.3855   $211.39   $211.40   $211.40  
  Purchase #7 $143.84   8.696%   $156.3483   $156.35   $156.35   $156.30  
  7 purchase totals = $1,050.47       $1,133.7203   $1,133.72   $1,133.70   $1,133.70