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 $116.49   8.701%   $126.6258   $126.63   $126.65   $126.60  
  Purchase #2 $81.74   4.347%   $85.2932   $85.29   $85.30   $85.30  
  Purchase #3 $106.49   11.708%   $118.9578   $118.96   $118.95   $119.00  
  Purchase #4 $186.81   11.720%   $208.7041   $208.70   $208.70   $208.70  
  Purchase #5 $186.68   7.825%   $201.2877   $201.29   $201.30   $201.30  
  Purchase #6 $93.92   13.506%   $106.6048   $106.60   $106.60   $106.60  
  Purchase #7 $227.77   10.348%   $251.3396   $251.34   $251.35   $251.30  
  7 purchase totals = $999.90       $1,098.8130   $1,098.81   $1,098.85   $1,098.80