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 $214.51   6.158%   $227.7195   $227.72   $227.70   $227.70  
  Purchase #2 $167.55   11.269%   $186.4312   $186.43   $186.45   $186.40  
  Purchase #3 $199.52   4.118%   $207.7362   $207.74   $207.75   $207.70  
  Purchase #4 $59.29   6.545%   $63.1705   $63.17   $63.15   $63.20  
  Purchase #5 $250.27   8.274%   $270.9773   $270.98   $271.00   $271.00  
  Purchase #6 $241.80   12.837%   $272.8399   $272.84   $272.85   $272.80  
  Purchase #7 $82.93   13.762%   $94.3428   $94.34   $94.35   $94.30  
  7 purchase totals = $1,215.87       $1,323.2174   $1,323.22   $1,323.25   $1,323.10