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 $235.76   11.569%   $263.0351   $263.04   $263.05   $263.00  
  Purchase #2 $160.90   10.415%   $177.6577   $177.66   $177.65   $177.70  
  Purchase #3 $43.64   3.584%   $45.2041   $45.20   $45.20   $45.20  
  Purchase #4 $25.69   8.648%   $27.9117   $27.91   $27.90   $27.90  
  Purchase #5 $58.77   12.377%   $66.044   $66.04   $66.05   $66.00  
  Purchase #6 $97.37   10.414%   $107.5101   $107.51   $107.50   $107.50  
  Purchase #7 $209.93   3.584%   $217.4539   $217.45   $217.45   $217.50  
  7 purchase totals = $832.06       $904.8166   $904.81   $904.80   $904.80