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 $222.92   10.163%   $245.5754   $245.58   $245.60   $245.60  
  Purchase #2 $144.31   10.109%   $158.8983   $158.90   $158.90   $158.90  
  Purchase #3 $45.93   10.325%   $50.6723   $50.67   $50.65   $50.70  
  Purchase #4 $215.92   5.494%   $227.7826   $227.78   $227.80   $227.80  
  Purchase #5 $248.55   3.430%   $257.0753   $257.08   $257.10   $257.10  
  Purchase #6 $88.44   9.612%   $96.9409   $96.94   $96.95   $96.90  
  Purchase #7 $230.92   5.476%   $243.5652   $243.57   $243.55   $243.60  
  7 purchase totals = $1,196.99       $1,280.5100   $1,280.52   $1,280.55   $1,280.60