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 $100.96   12.404%   $113.4831   $113.48   $113.50   $113.50  
  Purchase #2 $201.80   13.301%   $228.6414   $228.64   $228.65   $228.60  
  Purchase #3 $93.82   5.424%   $98.9088   $98.91   $98.90   $98.90  
  Purchase #4 $244.70   5.433%   $257.9946   $257.99   $258.00   $258.00  
  Purchase #5 $77.58   6.463%   $82.594   $82.59   $82.60   $82.60  
  Purchase #6 $76.25   6.552%   $81.2459   $81.25   $81.25   $81.20  
  Purchase #7 $182.71   4.562%   $191.0452   $191.05   $191.05   $191.00  
  7 purchase totals = $977.82       $1,053.9130   $1,053.91   $1,053.95   $1,053.80