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 $90.37   13.491%   $102.5618   $102.56   $102.55   $102.60  
  Purchase #2 $91.50   3.398%   $94.6092   $94.61   $94.60   $94.60  
  Purchase #3 $123.62   12.106%   $138.5854   $138.59   $138.60   $138.60  
  Purchase #4 $245.97   12.143%   $275.8381   $275.84   $275.85   $275.80  
  Purchase #5 $38.36   13.715%   $43.6211   $43.62   $43.60   $43.60  
  Purchase #6 $208.94   10.470%   $230.816   $230.82   $230.80   $230.80  
  Purchase #7 $146.93   11.284%   $163.5096   $163.51   $163.50   $163.50  
  7 purchase totals = $945.69       $1,049.5412   $1,049.55   $1,049.50   $1,049.50