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 $160.61   4.161%   $167.293   $167.29   $167.30   $167.30  
  Purchase #2 $102.71   12.362%   $115.407   $115.41   $115.40   $115.40  
  Purchase #3 $206.88   8.455%   $224.3717   $224.37   $224.35   $224.40  
  Purchase #4 $49.84   11.862%   $55.752   $55.75   $55.75   $55.80  
  Purchase #5 $129.72   3.699%   $134.5183   $134.52   $134.50   $134.50  
  Purchase #6 $159.34   7.293%   $170.9607   $170.96   $170.95   $171.00  
  Purchase #7 $153.89   7.802%   $165.8965   $165.90   $165.90   $165.90  
  7 purchase totals = $962.99       $1,034.1992   $1,034.20   $1,034.15   $1,034.30