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 $29.61   9.612%   $32.4561   $32.46   $32.45   $32.50  
  Purchase #2 $65.63   12.132%   $73.5922   $73.59   $73.60   $73.60  
  Purchase #3 $41.76   4.851%   $43.7858   $43.79   $43.80   $43.80  
  Purchase #4 $240.34   12.146%   $269.5317   $269.53   $269.55   $269.50  
  Purchase #5 $189.65   8.310%   $205.4099   $205.41   $205.40   $205.40  
  Purchase #6 $145.57   11.168%   $161.8273   $161.83   $161.85   $161.80  
  Purchase #7 $152.68   9.831%   $167.69   $167.69   $167.70   $167.70  
  7 purchase totals = $865.24       $954.2930   $954.30   $954.35   $954.30