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 $49.99   12.199%   $56.0883   $56.09   $56.10   $56.10  
  Purchase #2 $234.59   3.606%   $243.0493   $243.05   $243.05   $243.00  
  Purchase #3 $193.65   6.658%   $206.5432   $206.54   $206.55   $206.50  
  Purchase #4 $24.64   13.290%   $27.9147   $27.91   $27.90   $27.90  
  Purchase #5 $41.95   8.831%   $45.6546   $45.65   $45.65   $45.70  
  Purchase #6 $158.50   3.276%   $163.6925   $163.69   $163.70   $163.70  
  Purchase #7 $247.65   9.760%   $271.8206   $271.82   $271.80   $271.80  
  7 purchase totals = $950.97       $1,014.7632   $1,014.75   $1,014.75   $1,014.70