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 $64.56   7.252%   $69.2419   $69.24   $69.25   $69.20  
  Purchase #2 $173.27   10.406%   $191.3005   $191.30   $191.30   $191.30  
  Purchase #3 $10.77   3.423%   $11.1387   $11.14   $11.15   $11.10  
  Purchase #4 $130.27   3.105%   $134.3149   $134.31   $134.30   $134.30  
  Purchase #5 $122.52   5.427%   $129.1692   $129.17   $129.15   $129.20  
  Purchase #6 $247.25   8.751%   $268.8868   $268.89   $268.90   $268.90  
  Purchase #7 $182.62   5.689%   $193.0093   $193.01   $193.00   $193.00  
  7 purchase totals = $931.26       $997.0613   $997.06   $997.05   $997.00