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 $238.94   10.705%   $264.5185   $264.52   $264.50   $264.50  
  Purchase #2 $199.50   13.394%   $226.221   $226.22   $226.20   $226.20  
  Purchase #3 $73.90   9.269%   $80.7498   $80.75   $80.75   $80.70  
  Purchase #4 $216.65   11.714%   $242.0284   $242.03   $242.05   $242.00  
  Purchase #5 $138.99   7.836%   $149.8813   $149.88   $149.90   $149.90  
  Purchase #6 $190.30   12.426%   $213.9467   $213.95   $213.95   $213.90  
  Purchase #7 $137.84   8.480%   $149.5288   $149.53   $149.55   $149.50  
  7 purchase totals = $1,196.12       $1,326.8745   $1,326.88   $1,326.90   $1,326.70