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 $156.48   8.211%   $169.3286   $169.33   $169.35   $169.30  
  Purchase #2 $191.46   10.580%   $211.7165   $211.72   $211.70   $211.70  
  Purchase #3 $159.40   3.538%   $165.0396   $165.04   $165.05   $165.00  
  Purchase #4 $57.46   5.191%   $60.4427   $60.44   $60.45   $60.40  
  Purchase #5 $243.78   8.159%   $263.67   $263.67   $263.65   $263.70  
  Purchase #6 $16.35   7.145%   $17.5182   $17.52   $17.50   $17.50  
  Purchase #7 $137.71   6.185%   $146.2274   $146.23   $146.25   $146.20  
  7 purchase totals = $962.64       $1,033.9430   $1,033.95   $1,033.95   $1,033.80