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 $249.84   9.501%   $273.5773   $273.58   $273.60   $273.60  
  Purchase #2 $8.53   11.593%   $9.5189   $9.52   $9.50   $9.50  
  Purchase #3 $18.45   11.697%   $20.6081   $20.61   $20.60   $20.60  
  Purchase #4 $218.81   10.423%   $241.6166   $241.62   $241.60   $241.60  
  Purchase #5 $111.62   10.363%   $123.1872   $123.19   $123.20   $123.20  
  Purchase #6 $66.75   10.334%   $73.6479   $73.65   $73.65   $73.60  
  Purchase #7 $121.94   9.250%   $133.2195   $133.22   $133.20   $133.20  
  7 purchase totals = $795.94       $875.3755   $875.39   $875.35   $875.30