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 $59.71   6.207%   $63.4162   $63.42   $63.40   $63.40  
  Purchase #2 $98.93   7.808%   $106.6545   $106.65   $106.65   $106.70  
  Purchase #3 $153.69   13.545%   $174.5073   $174.51   $174.50   $174.50  
  Purchase #4 $148.59   8.145%   $160.6927   $160.69   $160.70   $160.70  
  Purchase #5 $123.49   7.119%   $132.2813   $132.28   $132.30   $132.30  
  Purchase #6 $135.87   8.416%   $147.3048   $147.30   $147.30   $147.30  
  Purchase #7 $201.93   3.713%   $209.4277   $209.43   $209.45   $209.40  
  7 purchase totals = $922.21       $994.2845   $994.28   $994.30   $994.30