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 $62.55   13.556%   $71.0293   $71.03   $71.05   $71.00  
  Purchase #2 $147.39   5.721%   $155.8222   $155.82   $155.80   $155.80  
  Purchase #3 $114.29   5.171%   $120.1999   $120.20   $120.20   $120.20  
  Purchase #4 $12.32   13.773%   $14.0168   $14.02   $14.00   $14.00  
  Purchase #5 $31.67   13.181%   $35.8444   $35.84   $35.85   $35.80  
  Purchase #6 $217.58   12.613%   $245.0234   $245.02   $245.00   $245.00  
  Purchase #7 $191.52   9.343%   $209.4137   $209.41   $209.40   $209.40  
  7 purchase totals = $777.32       $851.3497   $851.34   $851.30   $851.20