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 $231.32   9.662%   $253.6701   $253.67   $253.65   $253.70  
  Purchase #2 $203.95   7.302%   $218.8424   $218.84   $218.85   $218.80  
  Purchase #3 $157.76   11.461%   $175.8409   $175.84   $175.85   $175.80  
  Purchase #4 $32.61   7.188%   $34.954   $34.95   $34.95   $35.00  
  Purchase #5 $28.36   10.259%   $31.2695   $31.27   $31.25   $31.30  
  Purchase #6 $97.95   8.750%   $106.5206   $106.52   $106.50   $106.50  
  Purchase #7 $163.86   6.309%   $174.1979   $174.20   $174.20   $174.20  
  7 purchase totals = $915.81       $995.2954   $995.29   $995.25   $995.30