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 $64.95   13.240%   $73.5494   $73.55   $73.55   $73.50  
  Purchase #2 $166.73   6.278%   $177.1973   $177.20   $177.20   $177.20  
  Purchase #3 $240.52   13.459%   $272.8916   $272.89   $272.90   $272.90  
  Purchase #4 $129.27   6.256%   $137.3571   $137.36   $137.35   $137.40  
  Purchase #5 $214.53   4.619%   $224.4391   $224.44   $224.45   $224.40  
  Purchase #6 $159.85   13.828%   $181.9541   $181.95   $181.95   $182.00  
  Purchase #7 $94.37   13.145%   $106.7749   $106.77   $106.75   $106.80  
  7 purchase totals = $1,070.22       $1,174.1635   $1,174.16   $1,174.15   $1,174.20