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 $189.79   11.152%   $210.9554   $210.96   $210.95   $211.00  
  Purchase #2 $202.43   12.147%   $227.0192   $227.02   $227.00   $227.00  
  Purchase #3 $88.57   5.451%   $93.398   $93.40   $93.40   $93.40  
  Purchase #4 $35.79   12.262%   $40.1786   $40.18   $40.20   $40.20  
  Purchase #5 $212.98   11.589%   $237.6623   $237.66   $237.65   $237.70  
  Purchase #6 $177.77   12.268%   $199.5788   $199.58   $199.60   $199.60  
  Purchase #7 $186.56   8.527%   $202.468   $202.47   $202.45   $202.50  
  7 purchase totals = $1,093.89       $1,211.2603   $1,211.27   $1,211.25   $1,211.40