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 $80.52   5.603%   $85.0315   $85.03   $85.05   $85.00  
  Purchase #2 $216.34   5.552%   $228.3512   $228.35   $228.35   $228.40  
  Purchase #3 $21.67   12.381%   $24.353   $24.35   $24.35   $24.40  
  Purchase #4 $204.96   12.705%   $231.0002   $231.00   $231.00   $231.00  
  Purchase #5 $146.66   7.547%   $157.7284   $157.73   $157.75   $157.70  
  Purchase #6 $41.44   9.358%   $45.318   $45.32   $45.30   $45.30  
  Purchase #7 $117.89   5.127%   $123.9342   $123.93   $123.95   $123.90  
  7 purchase totals = $829.48       $895.7165   $895.71   $895.75   $895.70