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 $16.79   4.710%   $17.5808   $17.58   $17.60   $17.60  
  Purchase #2 $245.45   10.322%   $270.7853   $270.79   $270.80   $270.80  
  Purchase #3 $193.84   7.171%   $207.7403   $207.74   $207.75   $207.70  
  Purchase #4 $17.95   5.304%   $18.9021   $18.90   $18.90   $18.90  
  Purchase #5 $145.37   5.633%   $153.5587   $153.56   $153.55   $153.60  
  Purchase #6 $243.97   7.554%   $262.3995   $262.40   $262.40   $262.40  
  Purchase #7 $22.48   4.646%   $23.5244   $23.52   $23.50   $23.50  
  7 purchase totals = $885.85       $954.4911   $954.49   $954.50   $954.50