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 $221.57   5.590%   $233.9558   $233.96   $233.95   $234.00  
  Purchase #2 $138.46   6.655%   $147.6745   $147.67   $147.65   $147.70  
  Purchase #3 $170.52   6.747%   $182.025   $182.03   $182.05   $182.00  
  Purchase #4 $13.94   10.372%   $15.3859   $15.39   $15.40   $15.40  
  Purchase #5 $227.49   6.347%   $241.9288   $241.93   $241.95   $241.90  
  Purchase #6 $167.52   3.239%   $172.946   $172.95   $172.95   $172.90  
  Purchase #7 $30.43   10.747%   $33.7003   $33.70   $33.70   $33.70  
  7 purchase totals = $969.93       $1,027.6163   $1,027.63   $1,027.65   $1,027.60