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 $63.53   3.511%   $65.7605   $65.76   $65.75   $65.80  
  Purchase #2 $212.38   12.519%   $238.9679   $238.97   $238.95   $239.00  
  Purchase #3 $49.83   4.557%   $52.1008   $52.10   $52.10   $52.10  
  Purchase #4 $236.57   3.701%   $245.3255   $245.33   $245.35   $245.30  
  Purchase #5 $250.46   5.622%   $264.5409   $264.54   $264.55   $264.50  
  Purchase #6 $162.50   4.169%   $169.2746   $169.27   $169.25   $169.30  
  Purchase #7 $18.77   12.478%   $21.1121   $21.11   $21.10   $21.10  
  7 purchase totals = $994.04       $1,057.0823   $1,057.08   $1,057.05   $1,057.10