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 $57.89   6.286%   $61.529   $61.53   $61.55   $61.50  
  Purchase #2 $6.41   8.449%   $6.9516   $6.95   $6.95   $7.00  
  Purchase #3 $151.57   9.208%   $165.5266   $165.53   $165.55   $165.50  
  Purchase #4 $52.35   13.214%   $59.2675   $59.27   $59.25   $59.30  
  Purchase #5 $26.51   8.210%   $28.6865   $28.69   $28.70   $28.70  
  Purchase #6 $76.86   9.547%   $84.1978   $84.20   $84.20   $84.20  
  Purchase #7 $184.60   13.462%   $209.4509   $209.45   $209.45   $209.50  
  7 purchase totals = $556.19       $615.6099   $615.62   $615.65   $615.70