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 $153.38   4.825%   $160.7806   $160.78   $160.80   $160.80  
  Purchase #2 $107.50   13.570%   $122.0878   $122.09   $122.10   $122.10  
  Purchase #3 $229.61   8.453%   $249.0189   $249.02   $249.00   $249.00  
  Purchase #4 $193.34   10.844%   $214.3058   $214.31   $214.30   $214.30  
  Purchase #5 $162.90   5.705%   $172.1934   $172.19   $172.20   $172.20  
  Purchase #6 $80.45   8.466%   $87.2609   $87.26   $87.25   $87.30  
  Purchase #7 $78.83   6.396%   $83.872   $83.87   $83.85   $83.90  
  7 purchase totals = $1,006.01       $1,089.5194   $1,089.52   $1,089.50   $1,089.60