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 $114.73   6.352%   $122.0176   $122.02   $122.00   $122.00  
  Purchase #2 $230.94   6.822%   $246.6947   $246.69   $246.70   $246.70  
  Purchase #3 $56.55   6.437%   $60.1901   $60.19   $60.20   $60.20  
  Purchase #4 $115.95   6.282%   $123.234   $123.23   $123.25   $123.20  
  Purchase #5 $80.57   3.804%   $83.6349   $83.63   $83.65   $83.60  
  Purchase #6 $56.50   6.178%   $59.9906   $59.99   $60.00   $60.00  
  Purchase #7 $91.39   12.501%   $102.8147   $102.81   $102.80   $102.80  
  7 purchase totals = $746.63       $798.5766   $798.56   $798.60   $798.50