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 $169.87   8.347%   $184.049   $184.05   $184.05   $184.00  
  Purchase #2 $80.42   8.341%   $87.1278   $87.13   $87.15   $87.10  
  Purchase #3 $220.46   4.169%   $229.651   $229.65   $229.65   $229.70  
  Purchase #4 $222.58   3.456%   $230.2724   $230.27   $230.25   $230.30  
  Purchase #5 $163.69   7.850%   $176.5397   $176.54   $176.55   $176.50  
  Purchase #6 $73.60   9.732%   $80.7628   $80.76   $80.75   $80.80  
  Purchase #7 $11.45   11.776%   $12.7984   $12.80   $12.80   $12.80  
  7 purchase totals = $942.07       $1,001.2011   $1,001.20   $1,001.20   $1,001.20