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 $152.83   11.731%   $170.7585   $170.76   $170.75   $170.80  
  Purchase #2 $34.60   5.852%   $36.6248   $36.62   $36.60   $36.60  
  Purchase #3 $69.97   6.696%   $74.6552   $74.66   $74.65   $74.70  
  Purchase #4 $18.62   7.591%   $20.0334   $20.03   $20.05   $20.00  
  Purchase #5 $234.94   8.627%   $255.2083   $255.21   $255.20   $255.20  
  Purchase #6 $235.40   6.671%   $251.1035   $251.10   $251.10   $251.10  
  Purchase #7 $193.92   6.172%   $205.8887   $205.89   $205.90   $205.90  
  7 purchase totals = $940.28       $1,014.2724   $1,014.27   $1,014.25   $1,014.30