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 $49.66   5.182%   $52.2334   $52.23   $52.25   $52.20  
  Purchase #2 $232.79   13.326%   $263.8116   $263.81   $263.80   $263.80  
  Purchase #3 $62.52   9.537%   $68.4825   $68.48   $68.50   $68.50  
  Purchase #4 $53.88   13.273%   $61.0315   $61.03   $61.05   $61.00  
  Purchase #5 $185.95   5.283%   $195.7737   $195.77   $195.75   $195.80  
  Purchase #6 $180.28   13.474%   $204.5709   $204.57   $204.55   $204.60  
  Purchase #7 $5.67   7.234%   $6.0802   $6.08   $6.10   $6.10  
  7 purchase totals = $770.75       $851.9838   $851.97   $852.00   $852.00