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 $85.68   10.434%   $94.6199   $94.62   $94.60   $94.60  
  Purchase #2 $138.45   5.177%   $145.6176   $145.62   $145.60   $145.60  
  Purchase #3 $208.33   4.793%   $218.3153   $218.32   $218.30   $218.30  
  Purchase #4 $152.27   11.476%   $169.7445   $169.74   $169.75   $169.70  
  Purchase #5 $12.65   13.183%   $14.3176   $14.32   $14.30   $14.30  
  Purchase #6 $248.81   11.172%   $276.6071   $276.61   $276.60   $276.60  
  Purchase #7 $147.45   9.192%   $161.0036   $161.00   $161.00   $161.00  
  7 purchase totals = $993.64       $1,080.2256   $1,080.23   $1,080.15   $1,080.10