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 $59.75   9.791%   $65.6001   $65.60   $65.60   $65.60  
  Purchase #2 $221.51   7.396%   $237.8929   $237.89   $237.90   $237.90  
  Purchase #3 $109.68   7.492%   $117.8972   $117.90   $117.90   $117.90  
  Purchase #4 $209.74   10.244%   $231.2258   $231.23   $231.25   $231.20  
  Purchase #5 $59.68   10.623%   $66.0198   $66.02   $66.00   $66.00  
  Purchase #6 $194.46   13.650%   $221.0038   $221.00   $221.00   $221.00  
  Purchase #7 $164.92   10.322%   $181.943   $181.94   $181.95   $181.90  
  7 purchase totals = $1,019.74       $1,121.5826   $1,121.58   $1,121.60   $1,121.50