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 $77.98   13.183%   $88.2601   $88.26   $88.25   $88.30  
  Purchase #2 $179.92   7.656%   $193.6947   $193.69   $193.70   $193.70  
  Purchase #3 $86.35   4.179%   $89.9586   $89.96   $89.95   $90.00  
  Purchase #4 $235.86   3.127%   $243.2353   $243.24   $243.25   $243.20  
  Purchase #5 $184.52   5.308%   $194.3143   $194.31   $194.30   $194.30  
  Purchase #6 $106.62   12.784%   $120.2503   $120.25   $120.25   $120.30  
  Purchase #7 $208.62   11.868%   $233.379   $233.38   $233.40   $233.40  
  7 purchase totals = $1,079.87       $1,163.0923   $1,163.09   $1,163.10   $1,163.20