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 $31.86   5.625%   $33.6521   $33.65   $33.65   $33.70  
  Purchase #2 $241.81   13.858%   $275.32   $275.32   $275.30   $275.30  
  Purchase #3 $180.70   7.641%   $194.5073   $194.51   $194.50   $194.50  
  Purchase #4 $22.56   8.357%   $24.4453   $24.45   $24.45   $24.40  
  Purchase #5 $59.40   7.354%   $63.7683   $63.77   $63.75   $63.80  
  Purchase #6 $185.62   5.426%   $195.6917   $195.69   $195.70   $195.70  
  Purchase #7 $225.93   8.559%   $245.2673   $245.27   $245.25   $245.30  
  7 purchase totals = $947.88       $1,032.6520   $1,032.66   $1,032.60   $1,032.70