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 $65.70   7.651%   $70.7267   $70.73   $70.75   $70.70  
  Purchase #2 $125.55   7.388%   $134.8256   $134.83   $134.85   $134.80  
  Purchase #3 $157.54   11.294%   $175.3326   $175.33   $175.35   $175.30  
  Purchase #4 $161.81   9.671%   $177.4586   $177.46   $177.45   $177.50  
  Purchase #5 $114.26   5.458%   $120.4963   $120.50   $120.50   $120.50  
  Purchase #6 $202.81   8.632%   $220.3166   $220.32   $220.30   $220.30  
  Purchase #7 $45.40   13.120%   $51.3565   $51.36   $51.35   $51.40  
  7 purchase totals = $873.07       $950.5129   $950.53   $950.55   $950.50