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 $52.63   11.244%   $58.5477   $58.55   $58.55   $58.50  
  Purchase #2 $51.74   13.728%   $58.8429   $58.84   $58.85   $58.80  
  Purchase #3 $236.83   11.189%   $263.3289   $263.33   $263.35   $263.30  
  Purchase #4 $163.93   7.283%   $175.869   $175.87   $175.85   $175.90  
  Purchase #5 $136.40   7.828%   $147.0774   $147.08   $147.10   $147.10  
  Purchase #6 $18.85   7.374%   $20.24   $20.24   $20.25   $20.20  
  Purchase #7 $197.78   6.531%   $210.697   $210.70   $210.70   $210.70  
  7 purchase totals = $858.16       $934.6029   $934.61   $934.65   $934.50