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 $208.28   8.203%   $225.3652   $225.37   $225.35   $225.40  
  Purchase #2 $6.95   11.673%   $7.7613   $7.76   $7.75   $7.80  
  Purchase #3 $45.49   11.143%   $50.559   $50.56   $50.55   $50.60  
  Purchase #4 $59.63   8.426%   $64.6544   $64.65   $64.65   $64.70  
  Purchase #5 $110.43   13.846%   $125.7201   $125.72   $125.70   $125.70  
  Purchase #6 $242.77   12.222%   $272.4413   $272.44   $272.45   $272.40  
  Purchase #7 $232.58   8.472%   $252.2842   $252.28   $252.30   $252.30  
  7 purchase totals = $906.13       $998.7855   $998.78   $998.75   $998.90