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 $152.57   11.173%   $169.6166   $169.62   $169.60   $169.60  
  Purchase #2 $12.54   13.147%   $14.1886   $14.19   $14.20   $14.20  
  Purchase #3 $162.79   10.829%   $180.4185   $180.42   $180.40   $180.40  
  Purchase #4 $239.59   13.650%   $272.294   $272.29   $272.30   $272.30  
  Purchase #5 $120.33   6.862%   $128.587   $128.59   $128.60   $128.60  
  Purchase #6 $175.76   4.812%   $184.2176   $184.22   $184.20   $184.20  
  Purchase #7 $46.88   3.534%   $48.5367   $48.54   $48.55   $48.50  
  7 purchase totals = $910.46       $997.8590   $997.87   $997.85   $997.80