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 $218.93   10.320%   $241.5236   $241.52   $241.50   $241.50  
  Purchase #2 $76.98   13.466%   $87.3461   $87.35   $87.35   $87.30  
  Purchase #3 $7.74   3.187%   $7.9867   $7.99   $8.00   $8.00  
  Purchase #4 $31.36   4.748%   $32.849   $32.85   $32.85   $32.80  
  Purchase #5 $200.25   12.656%   $225.5936   $225.59   $225.60   $225.60  
  Purchase #6 $8.89   11.217%   $9.8872   $9.89   $9.90   $9.90  
  Purchase #7 $44.36   3.383%   $45.8607   $45.86   $45.85   $45.90  
  7 purchase totals = $588.51       $651.0469   $651.05   $651.05   $651.00