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 $226.26   6.719%   $241.4624   $241.46   $241.45   $241.50  
  Purchase #2 $200.98   12.847%   $226.7999   $226.80   $226.80   $226.80  
  Purchase #3 $49.81   11.380%   $55.4784   $55.48   $55.50   $55.50  
  Purchase #4 $42.35   6.625%   $45.1557   $45.16   $45.15   $45.20  
  Purchase #5 $61.68   3.667%   $63.9418   $63.94   $63.95   $63.90  
  Purchase #6 $166.51   13.740%   $189.3885   $189.39   $189.40   $189.40  
  Purchase #7 $12.39   3.533%   $12.8277   $12.83   $12.85   $12.80  
  7 purchase totals = $759.98       $835.0544   $835.06   $835.10   $835.10