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 $84.77   10.490%   $93.6624   $93.66   $93.65   $93.70  
  Purchase #2 $181.67   5.835%   $192.2704   $192.27   $192.25   $192.30  
  Purchase #3 $135.70   3.804%   $140.862   $140.86   $140.85   $140.90  
  Purchase #4 $108.50   3.588%   $112.393   $112.39   $112.40   $112.40  
  Purchase #5 $101.85   7.115%   $109.0966   $109.10   $109.10   $109.10  
  Purchase #6 $238.39   9.370%   $260.7271   $260.73   $260.75   $260.70  
  Purchase #7 $12.59   7.456%   $13.5287   $13.53   $13.55   $13.50  
  7 purchase totals = $863.47       $922.5402   $922.54   $922.55   $922.60