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 $14.77   12.437%   $16.6069   $16.61   $16.60   $16.60  
  Purchase #2 $61.99   6.466%   $65.9983   $66.00   $66.00   $66.00  
  Purchase #3 $216.47   10.123%   $238.3833   $238.38   $238.40   $238.40  
  Purchase #4 $194.50   13.844%   $221.4266   $221.43   $221.45   $221.40  
  Purchase #5 $51.30   7.474%   $55.1342   $55.13   $55.15   $55.10  
  Purchase #6 $182.62   9.779%   $200.4784   $200.48   $200.50   $200.50  
  Purchase #7 $209.69   9.160%   $228.8976   $228.90   $228.90   $228.90  
  7 purchase totals = $931.34       $1,026.9253   $1,026.93   $1,027.00   $1,026.90