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 $121.77   10.630%   $134.7142   $134.71   $134.70   $134.70  
  Purchase #2 $33.51   12.787%   $37.7949   $37.79   $37.80   $37.80  
  Purchase #3 $112.34   7.339%   $120.5846   $120.58   $120.60   $120.60  
  Purchase #4 $163.78   8.235%   $177.2673   $177.27   $177.25   $177.30  
  Purchase #5 $21.72   7.679%   $23.3879   $23.39   $23.40   $23.40  
  Purchase #6 $119.73   3.510%   $123.9325   $123.93   $123.95   $123.90  
  Purchase #7 $196.52   4.627%   $205.613   $205.61   $205.60   $205.60  
  7 purchase totals = $769.37       $823.2944   $823.28   $823.30   $823.30