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 $181.39   7.642%   $195.2518   $195.25   $195.25   $195.30  
  Purchase #2 $137.50   6.793%   $146.8404   $146.84   $146.85   $146.80  
  Purchase #3 $65.33   3.354%   $67.5212   $67.52   $67.50   $67.50  
  Purchase #4 $206.99   13.436%   $234.8012   $234.80   $234.80   $234.80  
  Purchase #5 $94.49   7.511%   $101.5871   $101.59   $101.60   $101.60  
  Purchase #6 $118.63   7.547%   $127.583   $127.58   $127.60   $127.60  
  Purchase #7 $116.34   4.616%   $121.7103   $121.71   $121.70   $121.70  
  7 purchase totals = $920.67       $995.2950   $995.29   $995.30   $995.30