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 $41.62   4.260%   $43.393   $43.39   $43.40   $43.40  
  Purchase #2 $146.58   4.807%   $153.6261   $153.63   $153.65   $153.60  
  Purchase #3 $235.25   7.356%   $252.555   $252.56   $252.55   $252.60  
  Purchase #4 $147.68   8.512%   $160.2505   $160.25   $160.25   $160.30  
  Purchase #5 $51.41   9.650%   $56.3711   $56.37   $56.35   $56.40  
  Purchase #6 $5.62   11.343%   $6.2575   $6.26   $6.25   $6.30  
  Purchase #7 $243.87   4.229%   $254.1833   $254.18   $254.20   $254.20  
  7 purchase totals = $872.03       $926.6365   $926.64   $926.65   $926.80