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 $49.92   13.186%   $56.5025   $56.50   $56.50   $56.50  
  Purchase #2 $96.99   9.289%   $105.9994   $106.00   $106.00   $106.00  
  Purchase #3 $109.64   9.551%   $120.1117   $120.11   $120.10   $120.10  
  Purchase #4 $24.52   11.840%   $27.4232   $27.42   $27.40   $27.40  
  Purchase #5 $32.29   6.178%   $34.2849   $34.28   $34.30   $34.30  
  Purchase #6 $220.37   12.646%   $248.238   $248.24   $248.25   $248.20  
  Purchase #7 $195.31   3.714%   $202.5638   $202.56   $202.55   $202.60  
  7 purchase totals = $729.04       $795.1235   $795.11   $795.10   $795.10