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 $56.35   5.304%   $59.3388   $59.34   $59.35   $59.30  
  Purchase #2 $181.65   3.355%   $187.7444   $187.74   $187.75   $187.70  
  Purchase #3 $226.99   10.586%   $251.0192   $251.02   $251.00   $251.00  
  Purchase #4 $186.74   3.371%   $193.035   $193.04   $193.05   $193.00  
  Purchase #5 $137.36   13.292%   $155.6179   $155.62   $155.60   $155.60  
  Purchase #6 $142.65   7.688%   $153.6169   $153.62   $153.60   $153.60  
  Purchase #7 $10.82   10.383%   $11.9434   $11.94   $11.95   $11.90  
  7 purchase totals = $942.56       $1,012.3156   $1,012.32   $1,012.30   $1,012.10