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 $116.62   7.256%   $125.0819   $125.08   $125.10   $125.10  
  Purchase #2 $182.87   13.469%   $207.5008   $207.50   $207.50   $207.50  
  Purchase #3 $163.93   6.440%   $174.4871   $174.49   $174.50   $174.50  
  Purchase #4 $129.32   8.717%   $140.5928   $140.59   $140.60   $140.60  
  Purchase #5 $163.59   11.753%   $182.8167   $182.82   $182.80   $182.80  
  Purchase #6 $52.27   4.592%   $54.6702   $54.67   $54.65   $54.70  
  Purchase #7 $65.44   12.635%   $73.7083   $73.71   $73.70   $73.70  
  7 purchase totals = $874.04       $958.8578   $958.86   $958.85   $958.90