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 $133.58   13.646%   $151.8083   $151.81   $151.80   $151.80  
  Purchase #2 $65.69   3.818%   $68.198   $68.20   $68.20   $68.20  
  Purchase #3 $146.64   8.198%   $158.6615   $158.66   $158.65   $158.70  
  Purchase #4 $222.83   7.569%   $239.696   $239.70   $239.70   $239.70  
  Purchase #5 $91.33   10.225%   $100.6685   $100.67   $100.65   $100.70  
  Purchase #6 $57.52   7.569%   $61.8737   $61.87   $61.85   $61.90  
  Purchase #7 $150.73   12.235%   $169.1718   $169.17   $169.15   $169.20  
  7 purchase totals = $868.32       $950.0778   $950.08   $950.00   $950.20