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 $58.50   10.671%   $64.7425   $64.74   $64.75   $64.70  
  Purchase #2 $227.52   6.560%   $242.4453   $242.45   $242.45   $242.40  
  Purchase #3 $180.85   13.732%   $205.6843   $205.68   $205.70   $205.70  
  Purchase #4 $223.40   6.780%   $238.5465   $238.55   $238.55   $238.50  
  Purchase #5 $11.27   11.730%   $12.592   $12.59   $12.60   $12.60  
  Purchase #6 $228.59   6.172%   $242.6986   $242.70   $242.70   $242.70  
  Purchase #7 $144.37   10.592%   $159.6617   $159.66   $159.65   $159.70  
  7 purchase totals = $1,074.50       $1,166.3709   $1,166.37   $1,166.40   $1,166.30