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 $61.87   7.256%   $66.3593   $66.36   $66.35   $66.40  
  Purchase #2 $118.83   12.853%   $134.1032   $134.10   $134.10   $134.10  
  Purchase #3 $203.89   12.166%   $228.6953   $228.70   $228.70   $228.70  
  Purchase #4 $52.67   7.296%   $56.5128   $56.51   $56.50   $56.50  
  Purchase #5 $213.26   12.152%   $239.1754   $239.18   $239.20   $239.20  
  Purchase #6 $184.28   8.345%   $199.6582   $199.66   $199.65   $199.70  
  Purchase #7 $150.55   11.223%   $167.4462   $167.45   $167.45   $167.40  
  7 purchase totals = $985.35       $1,091.9504   $1,091.96   $1,091.95   $1,092.00