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 $49.78   5.662%   $52.5985   $52.60   $52.60   $52.60  
  Purchase #2 $191.28   12.559%   $215.3029   $215.30   $215.30   $215.30  
  Purchase #3 $241.57   4.451%   $252.3223   $252.32   $252.30   $252.30  
  Purchase #4 $69.96   13.742%   $79.5739   $79.57   $79.55   $79.60  
  Purchase #5 $194.33   12.631%   $218.8758   $218.88   $218.90   $218.90  
  Purchase #6 $89.35   5.227%   $94.0203   $94.02   $94.00   $94.00  
  Purchase #7 $95.87   11.477%   $106.873   $106.87   $106.85   $106.90  
  7 purchase totals = $932.14       $1,019.5667   $1,019.56   $1,019.50   $1,019.60