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 $77.63   7.159%   $83.1875   $83.19   $83.20   $83.20  
  Purchase #2 $246.77   6.319%   $262.3634   $262.36   $262.35   $262.40  
  Purchase #3 $211.59   13.592%   $240.3493   $240.35   $240.35   $240.30  
  Purchase #4 $113.62   9.785%   $124.7377   $124.74   $124.75   $124.70  
  Purchase #5 $41.53   8.787%   $45.1792   $45.18   $45.20   $45.20  
  Purchase #6 $124.46   5.584%   $131.4098   $131.41   $131.40   $131.40  
  Purchase #7 $61.52   3.264%   $63.528   $63.53   $63.55   $63.50  
  7 purchase totals = $877.12       $950.7549   $950.76   $950.80   $950.70