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 $54.89   9.760%   $60.2473   $60.25   $60.25   $60.20  
  Purchase #2 $221.53   12.717%   $249.702   $249.70   $249.70   $249.70  
  Purchase #3 $98.52   11.382%   $109.7335   $109.73   $109.75   $109.70  
  Purchase #4 $234.56   12.250%   $263.2936   $263.29   $263.30   $263.30  
  Purchase #5 $100.51   5.382%   $105.9194   $105.92   $105.90   $105.90  
  Purchase #6 $155.44   7.765%   $167.5099   $167.51   $167.50   $167.50  
  Purchase #7 $22.91   3.235%   $23.6511   $23.65   $23.65   $23.70  
  7 purchase totals = $888.36       $980.0568   $980.05   $980.05   $980.00