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 $195.61   11.691%   $218.4788   $218.48   $218.50   $218.50  
  Purchase #2 $181.50   8.545%   $197.0092   $197.01   $197.00   $197.00  
  Purchase #3 $238.47   10.412%   $263.2995   $263.30   $263.30   $263.30  
  Purchase #4 $46.58   12.745%   $52.5166   $52.52   $52.50   $52.50  
  Purchase #5 $228.51   6.754%   $243.9436   $243.94   $243.95   $243.90  
  Purchase #6 $37.89   8.538%   $41.125   $41.13   $41.15   $41.10  
  Purchase #7 $222.88   7.476%   $239.5425   $239.54   $239.55   $239.50  
  7 purchase totals = $1,151.44       $1,255.9152   $1,255.92   $1,255.95   $1,255.80