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 $232.32   9.340%   $254.0187   $254.02   $254.00   $254.00  
  Purchase #2 $138.62   5.124%   $145.7229   $145.72   $145.70   $145.70  
  Purchase #3 $82.77   10.725%   $91.6471   $91.65   $91.65   $91.60  
  Purchase #4 $116.31   8.576%   $126.2847   $126.28   $126.30   $126.30  
  Purchase #5 $161.76   11.391%   $180.1861   $180.19   $180.20   $180.20  
  Purchase #6 $134.45   8.394%   $145.7357   $145.74   $145.75   $145.70  
  Purchase #7 $24.25   7.198%   $25.9955   $26.00   $26.00   $26.00  
  7 purchase totals = $890.48       $969.5907   $969.60   $969.60   $969.50