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 $147.52   8.860%   $160.5903   $160.59   $160.60   $160.60  
  Purchase #2 $54.87   6.721%   $58.5578   $58.56   $58.55   $58.60  
  Purchase #3 $33.86   11.404%   $37.7214   $37.72   $37.70   $37.70  
  Purchase #4 $58.47   8.611%   $63.5049   $63.50   $63.50   $63.50  
  Purchase #5 $153.93   6.828%   $164.4403   $164.44   $164.45   $164.40  
  Purchase #6 $8.60   11.747%   $9.6102   $9.61   $9.60   $9.60  
  Purchase #7 $110.52   6.293%   $117.475   $117.48   $117.50   $117.50  
  7 purchase totals = $567.77       $611.8999   $611.90   $611.90   $611.90