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 $104.79   5.259%   $110.3009   $110.30   $110.30   $110.30  
  Purchase #2 $221.50   11.552%   $247.0877   $247.09   $247.10   $247.10  
  Purchase #3 $72.66   9.162%   $79.3171   $79.32   $79.30   $79.30  
  Purchase #4 $157.33   11.808%   $175.9075   $175.91   $175.90   $175.90  
  Purchase #5 $184.58   6.353%   $196.3064   $196.31   $196.30   $196.30  
  Purchase #6 $27.88   13.483%   $31.6391   $31.64   $31.65   $31.60  
  Purchase #7 $39.40   12.244%   $44.2241   $44.22   $44.20   $44.20  
  7 purchase totals = $808.14       $884.7828   $884.79   $884.75   $884.70