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 $172.91   6.752%   $184.5849   $184.58   $184.60   $184.60  
  Purchase #2 $177.34   7.102%   $189.9347   $189.93   $189.95   $189.90  
  Purchase #3 $39.95   10.407%   $44.1076   $44.11   $44.10   $44.10  
  Purchase #4 $122.36   3.214%   $126.2927   $126.29   $126.30   $126.30  
  Purchase #5 $211.51   8.494%   $229.4757   $229.48   $229.50   $229.50  
  Purchase #6 $70.25   9.852%   $77.171   $77.17   $77.15   $77.20  
  Purchase #7 $153.55   8.269%   $166.247   $166.25   $166.25   $166.20  
  7 purchase totals = $947.87       $1,017.8136   $1,017.81   $1,017.85   $1,017.80