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 $30.77   6.214%   $32.682   $32.68   $32.70   $32.70  
  Purchase #2 $127.39   13.564%   $144.6692   $144.67   $144.65   $144.70  
  Purchase #3 $73.33   12.329%   $82.3709   $82.37   $82.35   $82.40  
  Purchase #4 $242.58   8.843%   $264.0313   $264.03   $264.05   $264.00  
  Purchase #5 $88.30   3.489%   $91.3808   $91.38   $91.40   $91.40  
  Purchase #6 $73.31   5.140%   $77.0781   $77.08   $77.10   $77.10  
  Purchase #7 $32.87   8.726%   $35.7382   $35.74   $35.75   $35.70  
  7 purchase totals = $668.55       $727.9505   $727.95   $728.00   $728.00