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 $27.37   11.507%   $30.5195   $30.52   $30.50   $30.50  
  Purchase #2 $208.54   11.584%   $232.6973   $232.70   $232.70   $232.70  
  Purchase #3 $39.65   11.770%   $44.3168   $44.32   $44.30   $44.30  
  Purchase #4 $124.51   10.169%   $137.1714   $137.17   $137.15   $137.20  
  Purchase #5 $202.59   11.330%   $225.5434   $225.54   $225.55   $225.50  
  Purchase #6 $44.82   6.811%   $47.8727   $47.87   $47.85   $47.90  
  Purchase #7 $226.39   3.155%   $233.5326   $233.53   $233.55   $233.50  
  7 purchase totals = $873.87       $951.6537   $951.65   $951.60   $951.60