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 $64.93   5.287%   $68.3628   $68.36   $68.35   $68.40  
  Purchase #2 $51.45   6.154%   $54.6162   $54.62   $54.60   $54.60  
  Purchase #3 $28.25   11.613%   $31.5307   $31.53   $31.55   $31.50  
  Purchase #4 $203.43   5.820%   $215.2696   $215.27   $215.25   $215.30  
  Purchase #5 $69.56   5.616%   $73.4665   $73.47   $73.45   $73.50  
  Purchase #6 $95.89   3.244%   $99.0007   $99.00   $99.00   $99.00  
  Purchase #7 $22.96   3.795%   $23.8313   $23.83   $23.85   $23.80  
  7 purchase totals = $536.47       $566.0778   $566.08   $566.05   $566.10