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 $63.49   8.351%   $68.792   $68.79   $68.80   $68.80  
  Purchase #2 $8.80   11.170%   $9.783   $9.78   $9.80   $9.80  
  Purchase #3 $221.31   6.196%   $235.0224   $235.02   $235.00   $235.00  
  Purchase #4 $32.64   7.125%   $34.9656   $34.97   $34.95   $35.00  
  Purchase #5 $69.85   5.178%   $73.4668   $73.47   $73.45   $73.50  
  Purchase #6 $212.33   4.779%   $222.4773   $222.48   $222.50   $222.50  
  Purchase #7 $182.57   12.431%   $205.2653   $205.27   $205.25   $205.30  
  7 purchase totals = $790.99       $849.7724   $849.78   $849.75   $849.90