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 $33.61   6.265%   $35.7157   $35.72   $35.70   $35.70  
  Purchase #2 $138.59   8.469%   $150.3272   $150.33   $150.35   $150.30  
  Purchase #3 $154.39   10.755%   $170.9946   $170.99   $171.00   $171.00  
  Purchase #4 $249.52   11.352%   $277.8455   $277.85   $277.85   $277.80  
  Purchase #5 $123.58   3.159%   $127.4839   $127.48   $127.50   $127.50  
  Purchase #6 $244.52   5.257%   $257.3744   $257.37   $257.35   $257.40  
  Purchase #7 $49.72   12.463%   $55.9166   $55.92   $55.90   $55.90  
  7 purchase totals = $993.93       $1,075.6579   $1,075.66   $1,075.65   $1,075.60