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 $26.63   13.752%   $30.2922   $30.29   $30.30   $30.30  
  Purchase #2 $60.53   5.192%   $63.6727   $63.67   $63.65   $63.70  
  Purchase #3 $232.72   9.170%   $254.0604   $254.06   $254.05   $254.10  
  Purchase #4 $106.82   4.326%   $111.441   $111.44   $111.45   $111.40  
  Purchase #5 $152.43   11.183%   $169.4762   $169.48   $169.50   $169.50  
  Purchase #6 $179.30   4.107%   $186.6639   $186.66   $186.65   $186.70  
  Purchase #7 $201.56   7.838%   $217.3583   $217.36   $217.35   $217.40  
  7 purchase totals = $959.99       $1,032.9647   $1,032.96   $1,032.95   $1,033.10