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 $82.48   13.456%   $93.5785   $93.58   $93.60   $93.60  
  Purchase #2 $208.90   6.394%   $222.2571   $222.26   $222.25   $222.30  
  Purchase #3 $236.65   4.320%   $246.8733   $246.87   $246.85   $246.90  
  Purchase #4 $153.52   4.473%   $160.3869   $160.39   $160.40   $160.40  
  Purchase #5 $201.38   12.261%   $226.0712   $226.07   $226.05   $226.10  
  Purchase #6 $52.74   9.858%   $57.9391   $57.94   $57.95   $57.90  
  Purchase #7 $78.69   10.555%   $86.9957   $87.00   $87.00   $87.00  
  7 purchase totals = $1,014.36       $1,094.1018   $1,094.11   $1,094.10   $1,094.20