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 $159.80   13.842%   $181.9195   $181.92   $181.90   $181.90  
  Purchase #2 $61.29   13.760%   $69.7235   $69.72   $69.70   $69.70  
  Purchase #3 $44.95   12.158%   $50.415   $50.42   $50.40   $50.40  
  Purchase #4 $166.53   9.163%   $181.7891   $181.79   $181.80   $181.80  
  Purchase #5 $140.30   5.234%   $147.6433   $147.64   $147.65   $147.60  
  Purchase #6 $185.66   10.578%   $205.2991   $205.30   $205.30   $205.30  
  Purchase #7 $123.38   10.627%   $136.4916   $136.49   $136.50   $136.50  
  7 purchase totals = $881.91       $973.2811   $973.28   $973.25   $973.20