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 $6.52   12.619%   $7.3428   $7.34   $7.35   $7.30  
  Purchase #2 $204.86   13.418%   $232.3481   $232.35   $232.35   $232.30  
  Purchase #3 $167.97   11.290%   $186.9338   $186.93   $186.95   $186.90  
  Purchase #4 $93.88   11.526%   $104.7006   $104.70   $104.70   $104.70  
  Purchase #5 $241.27   10.809%   $267.3489   $267.35   $267.35   $267.30  
  Purchase #6 $170.78   12.119%   $191.4768   $191.48   $191.50   $191.50  
  Purchase #7 $177.40   3.652%   $183.8786   $183.88   $183.90   $183.90  
  7 purchase totals = $1,062.68       $1,174.0296   $1,174.03   $1,174.10   $1,173.90