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 $189.65   8.181%   $205.1653   $205.17   $205.15   $205.20  
  Purchase #2 $166.67   4.226%   $173.7135   $173.71   $173.70   $173.70  
  Purchase #3 $203.88   11.135%   $226.582   $226.58   $226.60   $226.60  
  Purchase #4 $35.83   11.260%   $39.8645   $39.86   $39.85   $39.90  
  Purchase #5 $220.70   5.459%   $232.748   $232.75   $232.75   $232.70  
  Purchase #6 $197.93   10.725%   $219.158   $219.16   $219.15   $219.20  
  Purchase #7 $63.69   7.589%   $68.5234   $68.52   $68.50   $68.50  
  7 purchase totals = $1,078.35       $1,165.7547   $1,165.75   $1,165.70   $1,165.80