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 $245.46   9.647%   $269.1395   $269.14   $269.15   $269.10  
  Purchase #2 $145.87   7.329%   $156.5608   $156.56   $156.55   $156.60  
  Purchase #3 $7.74   13.436%   $8.7799   $8.78   $8.80   $8.80  
  Purchase #4 $132.26   7.121%   $141.6782   $141.68   $141.70   $141.70  
  Purchase #5 $243.55   11.192%   $270.8081   $270.81   $270.80   $270.80  
  Purchase #6 $122.50   6.375%   $130.3094   $130.31   $130.30   $130.30  
  Purchase #7 $61.58   11.630%   $68.7418   $68.74   $68.75   $68.70  
  7 purchase totals = $958.96       $1,046.0177   $1,046.02   $1,046.05   $1,046.00