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 $59.59   12.566%   $67.0781   $67.08   $67.10   $67.10  
  Purchase #2 $201.98   8.716%   $219.5846   $219.58   $219.60   $219.60  
  Purchase #3 $123.82   8.609%   $134.4797   $134.48   $134.50   $134.50  
  Purchase #4 $234.32   6.520%   $249.5977   $249.60   $249.60   $249.60  
  Purchase #5 $152.46   7.427%   $163.7832   $163.78   $163.80   $163.80  
  Purchase #6 $128.36   6.640%   $136.8831   $136.88   $136.90   $136.90  
  Purchase #7 $167.79   13.347%   $190.1849   $190.18   $190.20   $190.20  
  7 purchase totals = $1,068.32       $1,161.5913   $1,161.58   $1,161.70   $1,161.70