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 $217.48   9.684%   $238.5408   $238.54   $238.55   $238.50  
  Purchase #2 $126.76   12.544%   $142.6608   $142.66   $142.65   $142.70  
  Purchase #3 $236.49   13.774%   $269.0641   $269.06   $269.05   $269.10  
  Purchase #4 $44.88   10.247%   $49.4789   $49.48   $49.50   $49.50  
  Purchase #5 $249.55   7.328%   $267.837   $267.84   $267.85   $267.80  
  Purchase #6 $48.89   3.782%   $50.739   $50.74   $50.75   $50.70  
  Purchase #7 $134.81   11.415%   $150.1986   $150.20   $150.20   $150.20  
  7 purchase totals = $1,058.86       $1,168.5192   $1,168.52   $1,168.55   $1,168.50