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 $33.42   3.428%   $34.5656   $34.57   $34.55   $34.60  
  Purchase #2 $10.90   6.583%   $11.6175   $11.62   $11.60   $11.60  
  Purchase #3 $213.89   10.782%   $236.9516   $236.95   $236.95   $237.00  
  Purchase #4 $212.49   10.739%   $235.3093   $235.31   $235.30   $235.30  
  Purchase #5 $49.83   5.761%   $52.7007   $52.70   $52.70   $52.70  
  Purchase #6 $109.44   9.547%   $119.8882   $119.89   $119.90   $119.90  
  Purchase #7 $230.51   9.107%   $251.5025   $251.50   $251.50   $251.50  
  7 purchase totals = $860.48       $942.5354   $942.54   $942.50   $942.60