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 $106.58   11.201%   $118.518   $118.52   $118.50   $118.50  
  Purchase #2 $168.54   13.153%   $190.7081   $190.71   $190.70   $190.70  
  Purchase #3 $231.93   11.795%   $259.2861   $259.29   $259.30   $259.30  
  Purchase #4 $222.78   7.442%   $239.3593   $239.36   $239.35   $239.40  
  Purchase #5 $205.42   13.814%   $233.7967   $233.80   $233.80   $233.80  
  Purchase #6 $73.48   9.589%   $80.526   $80.53   $80.55   $80.50  
  Purchase #7 $163.28   10.224%   $179.9737   $179.97   $179.95   $180.00  
  7 purchase totals = $1,172.01       $1,302.1679   $1,302.18   $1,302.15   $1,302.20