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 $214.84   9.837%   $235.9738   $235.97   $235.95   $236.00  
  Purchase #2 $54.52   11.263%   $60.6606   $60.66   $60.65   $60.70  
  Purchase #3 $212.87   8.408%   $230.7681   $230.77   $230.75   $230.80  
  Purchase #4 $206.25   5.539%   $217.6742   $217.67   $217.65   $217.70  
  Purchase #5 $118.27   10.784%   $131.0242   $131.02   $131.00   $131.00  
  Purchase #6 $155.93   9.686%   $171.0334   $171.03   $171.05   $171.00  
  Purchase #7 $231.93   11.517%   $258.6414   $258.64   $258.65   $258.60  
  7 purchase totals = $1,194.61       $1,305.7757   $1,305.76   $1,305.70   $1,305.80