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 $76.51   11.348%   $85.1924   $85.19   $85.20   $85.20  
  Purchase #2 $132.55   6.144%   $140.6939   $140.69   $140.70   $140.70  
  Purchase #3 $209.84   12.118%   $235.2684   $235.27   $235.25   $235.30  
  Purchase #4 $130.81   13.396%   $148.3333   $148.33   $148.35   $148.30  
  Purchase #5 $201.55   5.435%   $212.5042   $212.50   $212.50   $212.50  
  Purchase #6 $37.39   5.742%   $39.5369   $39.54   $39.55   $39.50  
  Purchase #7 $145.67   7.177%   $156.1247   $156.12   $156.10   $156.10  
  7 purchase totals = $934.32       $1,017.6538   $1,017.64   $1,017.65   $1,017.60