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 $62.65   10.281%   $69.091   $69.09   $69.10   $69.10  
  Purchase #2 $145.37   3.302%   $150.1701   $150.17   $150.15   $150.20  
  Purchase #3 $205.89   8.464%   $223.3165   $223.32   $223.30   $223.30  
  Purchase #4 $48.84   7.119%   $52.3169   $52.32   $52.30   $52.30  
  Purchase #5 $111.62   10.190%   $122.9941   $122.99   $123.00   $123.00  
  Purchase #6 $60.87   12.419%   $68.4294   $68.43   $68.45   $68.40  
  Purchase #7 $17.91   4.143%   $18.652   $18.65   $18.65   $18.70  
  7 purchase totals = $653.15       $704.9700   $704.97   $704.95   $705.00