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 $166.79   10.467%   $184.2479   $184.25   $184.25   $184.20  
  Purchase #2 $40.62   5.151%   $42.7123   $42.71   $42.70   $42.70  
  Purchase #3 $151.65   13.120%   $171.5465   $171.55   $171.55   $171.50  
  Purchase #4 $138.35   10.423%   $152.7702   $152.77   $152.75   $152.80  
  Purchase #5 $245.29   3.199%   $253.1368   $253.14   $253.15   $253.10  
  Purchase #6 $246.26   6.492%   $262.2472   $262.25   $262.25   $262.20  
  Purchase #7 $203.86   12.243%   $228.8186   $228.82   $228.80   $228.80  
  7 purchase totals = $1,192.82       $1,295.4795   $1,295.49   $1,295.45   $1,295.30