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 $109.33   13.140%   $123.696   $123.70   $123.70   $123.70  
  Purchase #2 $80.78   8.625%   $87.7473   $87.75   $87.75   $87.70  
  Purchase #3 $73.70   6.167%   $78.2451   $78.25   $78.25   $78.20  
  Purchase #4 $245.85   9.703%   $269.7048   $269.70   $269.70   $269.70  
  Purchase #5 $110.67   11.820%   $123.7512   $123.75   $123.75   $123.80  
  Purchase #6 $211.36   12.439%   $237.6511   $237.65   $237.65   $237.70  
  Purchase #7 $122.26   11.458%   $136.2686   $136.27   $136.25   $136.30  
  7 purchase totals = $953.95       $1,057.0641   $1,057.07   $1,057.05   $1,057.10