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 $49.45   4.469%   $51.6599   $51.66   $51.65   $51.70  
  Purchase #2 $5.66   5.202%   $5.9544   $5.95   $5.95   $6.00  
  Purchase #3 $244.85   7.409%   $262.9909   $262.99   $263.00   $263.00  
  Purchase #4 $205.68   12.408%   $231.2008   $231.20   $231.20   $231.20  
  Purchase #5 $41.87   5.104%   $44.007   $44.01   $44.00   $44.00  
  Purchase #6 $148.77   4.703%   $155.7667   $155.77   $155.75   $155.80  
  Purchase #7 $184.91   8.510%   $200.6458   $200.65   $200.65   $200.60  
  7 purchase totals = $881.19       $952.2255   $952.23   $952.20   $952.30