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 $175.59   4.816%   $184.0464   $184.05   $184.05   $184.00  
  Purchase #2 $18.53   6.798%   $19.7897   $19.79   $19.80   $19.80  
  Purchase #3 $216.95   4.255%   $226.1812   $226.18   $226.20   $226.20  
  Purchase #4 $103.93   5.261%   $109.3978   $109.40   $109.40   $109.40  
  Purchase #5 $63.99   6.567%   $68.1922   $68.19   $68.20   $68.20  
  Purchase #6 $85.34   6.263%   $90.6848   $90.68   $90.70   $90.70  
  Purchase #7 $43.36   5.676%   $45.8211   $45.82   $45.80   $45.80  
  7 purchase totals = $707.69       $744.1132   $744.11   $744.15   $744.10