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 $23.72   13.398%   $26.898   $26.90   $26.90   $26.90  
  Purchase #2 $31.69   8.411%   $34.3554   $34.36   $34.35   $34.40  
  Purchase #3 $208.95   6.246%   $222.001   $222.00   $222.00   $222.00  
  Purchase #4 $41.96   5.401%   $44.2263   $44.23   $44.25   $44.20  
  Purchase #5 $209.85   6.502%   $223.4944   $223.49   $223.50   $223.50  
  Purchase #6 $153.52   6.122%   $162.9185   $162.92   $162.90   $162.90  
  Purchase #7 $200.91   12.579%   $226.1825   $226.18   $226.20   $226.20  
  7 purchase totals = $870.60       $940.0761   $940.08   $940.10   $940.10