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 $123.41   8.773%   $134.2368   $134.24   $134.25   $134.20  
  Purchase #2 $117.26   13.136%   $132.6633   $132.66   $132.65   $132.70  
  Purchase #3 $201.94   10.272%   $222.6833   $222.68   $222.70   $222.70  
  Purchase #4 $56.68   9.406%   $62.0113   $62.01   $62.00   $62.00  
  Purchase #5 $140.46   8.244%   $152.0395   $152.04   $152.05   $152.00  
  Purchase #6 $35.68   4.400%   $37.2499   $37.25   $37.25   $37.20  
  Purchase #7 $159.93   6.513%   $170.3462   $170.35   $170.35   $170.30  
  7 purchase totals = $835.36       $911.2303   $911.23   $911.25   $911.10