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 $46.99   3.152%   $48.4711   $48.47   $48.45   $48.50  
  Purchase #2 $145.33   7.608%   $156.3867   $156.39   $156.40   $156.40  
  Purchase #3 $110.94   12.262%   $124.5435   $124.54   $124.55   $124.50  
  Purchase #4 $56.33   12.727%   $63.4991   $63.50   $63.50   $63.50  
  Purchase #5 $66.52   3.671%   $68.9619   $68.96   $68.95   $69.00  
  Purchase #6 $147.26   5.812%   $155.8188   $155.82   $155.80   $155.80  
  Purchase #7 $202.89   13.813%   $230.9152   $230.92   $230.90   $230.90  
  7 purchase totals = $776.26       $848.5963   $848.60   $848.55   $848.60