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 $216.91   8.160%   $234.6099   $234.61   $234.60   $234.60  
  Purchase #2 $70.99   4.712%   $74.335   $74.34   $74.35   $74.30  
  Purchase #3 $70.55   13.168%   $79.84   $79.84   $79.85   $79.80  
  Purchase #4 $203.26   3.336%   $210.0408   $210.04   $210.05   $210.00  
  Purchase #5 $135.42   5.332%   $142.6406   $142.64   $142.65   $142.60  
  Purchase #6 $232.41   8.590%   $252.374   $252.37   $252.35   $252.40  
  Purchase #7 $233.30   3.746%   $242.0394   $242.04   $242.05   $242.00  
  7 purchase totals = $1,162.84       $1,235.8797   $1,235.88   $1,235.90   $1,235.70