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 $182.58   12.250%   $204.9461   $204.95   $204.95   $204.90  
  Purchase #2 $116.95   10.193%   $128.8707   $128.87   $128.85   $128.90  
  Purchase #3 $114.82   5.792%   $121.4704   $121.47   $121.45   $121.50  
  Purchase #4 $81.56   4.603%   $85.3142   $85.31   $85.30   $85.30  
  Purchase #5 $171.65   5.375%   $180.8762   $180.88   $180.90   $180.90  
  Purchase #6 $158.52   10.405%   $175.014   $175.01   $175.00   $175.00  
  Purchase #7 $108.26   8.612%   $117.5834   $117.58   $117.60   $117.60  
  7 purchase totals = $934.34       $1,014.0750   $1,014.07   $1,014.05   $1,014.10