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 $244.33   3.257%   $252.2878   $252.29   $252.30   $252.30  
  Purchase #2 $85.70   11.841%   $95.8477   $95.85   $95.85   $95.80  
  Purchase #3 $105.67   11.722%   $118.0566   $118.06   $118.05   $118.10  
  Purchase #4 $22.62   10.230%   $24.934   $24.93   $24.95   $24.90  
  Purchase #5 $239.58   12.372%   $269.2208   $269.22   $269.20   $269.20  
  Purchase #6 $46.34   5.680%   $48.9721   $48.97   $48.95   $49.00  
  Purchase #7 $234.33   3.495%   $242.5198   $242.52   $242.50   $242.50  
  7 purchase totals = $978.57       $1,051.8388   $1,051.84   $1,051.80   $1,051.80