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 $148.87   8.136%   $160.9821   $160.98   $161.00   $161.00  
  Purchase #2 $96.69   13.635%   $109.8737   $109.87   $109.85   $109.90  
  Purchase #3 $24.59   7.311%   $26.3878   $26.39   $26.40   $26.40  
  Purchase #4 $219.31   6.192%   $232.8897   $232.89   $232.90   $232.90  
  Purchase #5 $163.84   3.154%   $169.0075   $169.01   $169.00   $169.00  
  Purchase #6 $178.45   11.791%   $199.491   $199.49   $199.50   $199.50  
  Purchase #7 $129.82   5.420%   $136.8562   $136.86   $136.85   $136.90  
  7 purchase totals = $961.57       $1,035.4880   $1,035.49   $1,035.50   $1,035.60