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 $50.82   9.363%   $55.5783   $55.58   $55.60   $55.60  
  Purchase #2 $134.58   11.261%   $149.7351   $149.74   $149.75   $149.70  
  Purchase #3 $77.96   3.377%   $80.5927   $80.59   $80.60   $80.60  
  Purchase #4 $174.51   11.684%   $194.8997   $194.90   $194.90   $194.90  
  Purchase #5 $72.92   5.578%   $76.9875   $76.99   $77.00   $77.00  
  Purchase #6 $240.34   10.617%   $265.8569   $265.86   $265.85   $265.90  
  Purchase #7 $216.28   8.517%   $234.7006   $234.70   $234.70   $234.70  
  7 purchase totals = $967.41       $1,058.3508   $1,058.36   $1,058.40   $1,058.40