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 $38.93   13.390%   $44.1427   $44.14   $44.15   $44.10  
  Purchase #2 $172.42   3.580%   $178.5926   $178.59   $178.60   $178.60  
  Purchase #3 $53.47   11.550%   $59.6458   $59.65   $59.65   $59.60  
  Purchase #4 $205.36   9.813%   $225.512   $225.51   $225.50   $225.50  
  Purchase #5 $174.34   10.505%   $192.6544   $192.65   $192.65   $192.70  
  Purchase #6 $217.49   5.592%   $229.652   $229.65   $229.65   $229.70  
  Purchase #7 $42.62   7.835%   $45.9593   $45.96   $45.95   $46.00  
  7 purchase totals = $904.63       $976.1588   $976.15   $976.15   $976.20