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 $192.82   8.724%   $209.6416   $209.64   $209.65   $209.60  
  Purchase #2 $85.81   12.419%   $96.4667   $96.47   $96.45   $96.50  
  Purchase #3 $246.57   4.471%   $257.5941   $257.59   $257.60   $257.60  
  Purchase #4 $154.76   8.478%   $167.8806   $167.88   $167.90   $167.90  
  Purchase #5 $212.63   13.227%   $240.7546   $240.75   $240.75   $240.80  
  Purchase #6 $12.40   9.354%   $13.5599   $13.56   $13.55   $13.60  
  Purchase #7 $71.61   3.488%   $74.1078   $74.11   $74.10   $74.10  
  7 purchase totals = $976.60       $1,060.0053   $1,060.00   $1,060.00   $1,060.10