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 $89.97   12.569%   $101.2783   $101.28   $101.30   $101.30  
  Purchase #2 $200.80   10.566%   $222.0165   $222.02   $222.00   $222.00  
  Purchase #3 $164.88   10.132%   $181.5856   $181.59   $181.60   $181.60  
  Purchase #4 $166.26   6.662%   $177.3362   $177.34   $177.35   $177.30  
  Purchase #5 $41.66   3.711%   $43.206   $43.21   $43.20   $43.20  
  Purchase #6 $16.46   12.862%   $18.5771   $18.58   $18.60   $18.60  
  Purchase #7 $194.67   8.649%   $211.507   $211.51   $211.50   $211.50  
  7 purchase totals = $874.70       $955.5067   $955.53   $955.55   $955.50