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 $190.27   11.258%   $211.6906   $211.69   $211.70   $211.70  
  Purchase #2 $50.85   3.470%   $52.6145   $52.61   $52.60   $52.60  
  Purchase #3 $131.59   11.780%   $147.0913   $147.09   $147.10   $147.10  
  Purchase #4 $243.81   5.868%   $258.1168   $258.12   $258.10   $258.10  
  Purchase #5 $121.39   11.511%   $135.3632   $135.36   $135.35   $135.40  
  Purchase #6 $49.53   13.792%   $56.3612   $56.36   $56.35   $56.40  
  Purchase #7 $147.70   10.364%   $163.0076   $163.01   $163.00   $163.00  
  7 purchase totals = $935.14       $1,024.2452   $1,024.24   $1,024.20   $1,024.30