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 $248.39   5.864%   $262.9556   $262.96   $262.95   $263.00  
  Purchase #2 $189.46   6.197%   $201.2008   $201.20   $201.20   $201.20  
  Purchase #3 $27.74   5.654%   $29.3084   $29.31   $29.30   $29.30  
  Purchase #4 $11.26   7.388%   $12.0919   $12.09   $12.10   $12.10  
  Purchase #5 $12.94   11.311%   $14.4036   $14.40   $14.40   $14.40  
  Purchase #6 $211.52   8.424%   $229.3384   $229.34   $229.35   $229.30  
  Purchase #7 $91.66   6.369%   $97.4978   $97.50   $97.50   $97.50  
  7 purchase totals = $792.97       $846.7965   $846.80   $846.80   $846.80