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 $133.61   12.626%   $150.4796   $150.48   $150.50   $150.50  
  Purchase #2 $131.85   8.724%   $143.3526   $143.35   $143.35   $143.40  
  Purchase #3 $125.51   3.841%   $130.3308   $130.33   $130.35   $130.30  
  Purchase #4 $184.64   11.531%   $205.9308   $205.93   $205.95   $205.90  
  Purchase #5 $159.30   6.454%   $169.5812   $169.58   $169.60   $169.60  
  Purchase #6 $188.52   8.582%   $204.6988   $204.70   $204.70   $204.70  
  Purchase #7 $151.50   6.605%   $161.5066   $161.51   $161.50   $161.50  
  7 purchase totals = $1,074.93       $1,165.8804   $1,165.88   $1,165.95   $1,165.90