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 $211.70   11.124%   $235.2495   $235.25   $235.25   $235.20  
  Purchase #2 $93.68   4.623%   $98.0108   $98.01   $98.00   $98.00  
  Purchase #3 $61.93   6.254%   $65.8031   $65.80   $65.80   $65.80  
  Purchase #4 $94.32   5.855%   $99.8424   $99.84   $99.85   $99.80  
  Purchase #5 $113.25   4.190%   $117.9952   $118.00   $118.00   $118.00  
  Purchase #6 $134.76   3.552%   $139.5467   $139.55   $139.55   $139.50  
  Purchase #7 $48.98   12.461%   $55.0834   $55.08   $55.10   $55.10  
  7 purchase totals = $758.62       $811.5311   $811.53   $811.55   $811.40