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 $204.28   13.798%   $232.4666   $232.47   $232.45   $232.50  
  Purchase #2 $194.80   12.241%   $218.6455   $218.65   $218.65   $218.60  
  Purchase #3 $172.77   11.557%   $192.737   $192.74   $192.75   $192.70  
  Purchase #4 $205.48   9.599%   $225.204   $225.20   $225.20   $225.20  
  Purchase #5 $91.76   12.403%   $103.141   $103.14   $103.15   $103.10  
  Purchase #6 $205.30   11.581%   $229.0758   $229.08   $229.10   $229.10  
  Purchase #7 $207.92   12.614%   $234.147   $234.15   $234.15   $234.10  
  7 purchase totals = $1,282.31       $1,435.4169   $1,435.43   $1,435.45   $1,435.30