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 $38.86   5.796%   $41.1123   $41.11   $41.10   $41.10  
  Purchase #2 $212.51   6.640%   $226.6207   $226.62   $226.60   $226.60  
  Purchase #3 $100.40   12.665%   $113.1157   $113.12   $113.10   $113.10  
  Purchase #4 $10.27   13.275%   $11.6333   $11.63   $11.65   $11.60  
  Purchase #5 $194.44   12.838%   $219.4022   $219.40   $219.40   $219.40  
  Purchase #6 $162.44   5.574%   $171.4944   $171.49   $171.50   $171.50  
  Purchase #7 $161.65   9.629%   $177.2153   $177.22   $177.20   $177.20  
  7 purchase totals = $880.57       $960.5939   $960.59   $960.55   $960.50