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 $101.94   7.556%   $109.6426   $109.64   $109.65   $109.60  
  Purchase #2 $61.95   3.232%   $63.9522   $63.95   $63.95   $64.00  
  Purchase #3 $202.93   6.453%   $216.0251   $216.03   $216.05   $216.00  
  Purchase #4 $241.31   4.458%   $252.0676   $252.07   $252.05   $252.10  
  Purchase #5 $20.51   6.624%   $21.8686   $21.87   $21.85   $21.90  
  Purchase #6 $183.98   8.447%   $199.5208   $199.52   $199.50   $199.50  
  Purchase #7 $105.89   12.383%   $119.0024   $119.00   $119.00   $119.00  
  7 purchase totals = $918.51       $982.0793   $982.08   $982.05   $982.10