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 $208.41   10.519%   $230.3326   $230.33   $230.35   $230.30  
  Purchase #2 $187.33   7.706%   $201.7656   $201.77   $201.75   $201.80  
  Purchase #3 $234.66   12.360%   $263.664   $263.66   $263.65   $263.70  
  Purchase #4 $21.47   6.432%   $22.851   $22.85   $22.85   $22.90  
  Purchase #5 $184.95   10.227%   $203.8648   $203.86   $203.85   $203.90  
  Purchase #6 $42.61   3.410%   $44.063   $44.06   $44.05   $44.10  
  Purchase #7 $45.94   4.604%   $48.0551   $48.06   $48.05   $48.10  
  7 purchase totals = $925.37       $1,014.5961   $1,014.59   $1,014.55   $1,014.80