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 $48.82   9.710%   $53.5604   $53.56   $53.55   $53.60  
  Purchase #2 $181.78   6.426%   $193.4612   $193.46   $193.45   $193.50  
  Purchase #3 $203.60   11.133%   $226.2668   $226.27   $226.25   $226.30  
  Purchase #4 $147.31   9.720%   $161.6285   $161.63   $161.65   $161.60  
  Purchase #5 $32.63   6.708%   $34.8188   $34.82   $34.80   $34.80  
  Purchase #6 $179.71   8.314%   $194.6511   $194.65   $194.65   $194.70  
  Purchase #7 $137.48   7.189%   $147.3634   $147.36   $147.35   $147.40  
  7 purchase totals = $931.33       $1,011.7502   $1,011.75   $1,011.70   $1,011.90