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 $61.74   9.262%   $67.4584   $67.46   $67.45   $67.50  
  Purchase #2 $183.38   10.672%   $202.9503   $202.95   $202.95   $203.00  
  Purchase #3 $241.46   9.800%   $265.1231   $265.12   $265.10   $265.10  
  Purchase #4 $126.89   8.218%   $137.3178   $137.32   $137.30   $137.30  
  Purchase #5 $36.37   7.713%   $39.1752   $39.18   $39.20   $39.20  
  Purchase #6 $222.71   3.778%   $231.124   $231.12   $231.10   $231.10  
  Purchase #7 $94.81   8.409%   $102.7826   $102.78   $102.80   $102.80  
  7 purchase totals = $967.36       $1,045.9314   $1,045.93   $1,045.90   $1,046.00