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 $62.61   12.606%   $70.5026   $70.50   $70.50   $70.50  
  Purchase #2 $111.45   6.179%   $118.3365   $118.34   $118.35   $118.30  
  Purchase #3 $248.80   7.436%   $267.3008   $267.30   $267.30   $267.30  
  Purchase #4 $58.39   10.479%   $64.5087   $64.51   $64.50   $64.50  
  Purchase #5 $142.39   4.217%   $148.3946   $148.39   $148.40   $148.40  
  Purchase #6 $95.98   6.394%   $102.117   $102.12   $102.10   $102.10  
  Purchase #7 $168.48   7.770%   $181.5709   $181.57   $181.55   $181.60  
  7 purchase totals = $888.10       $952.7311   $952.73   $952.70   $952.70