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 $200.98   13.459%   $228.0299   $228.03   $228.05   $228.00  
  Purchase #2 $146.32   8.689%   $159.0337   $159.03   $159.05   $159.00  
  Purchase #3 $212.45   11.653%   $237.2068   $237.21   $237.20   $237.20  
  Purchase #4 $177.29   10.285%   $195.5243   $195.52   $195.50   $195.50  
  Purchase #5 $163.96   8.102%   $177.244   $177.24   $177.25   $177.20  
  Purchase #6 $17.45   3.153%   $18.0002   $18.00   $18.00   $18.00  
  Purchase #7 $196.86   7.691%   $212.0005   $212.00   $212.00   $212.00  
  7 purchase totals = $1,115.31       $1,227.0394   $1,227.03   $1,227.05   $1,226.90