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 $211.46   10.614%   $233.9044   $233.90   $233.90   $233.90  
  Purchase #2 $226.96   12.320%   $254.9215   $254.92   $254.90   $254.90  
  Purchase #3 $147.47   4.386%   $153.938   $153.94   $153.95   $153.90  
  Purchase #4 $237.88   9.118%   $259.5699   $259.57   $259.55   $259.60  
  Purchase #5 $70.57   7.786%   $76.0646   $76.06   $76.05   $76.10  
  Purchase #6 $147.50   10.227%   $162.5848   $162.58   $162.60   $162.60  
  Purchase #7 $80.44   9.762%   $88.2926   $88.29   $88.30   $88.30  
  7 purchase totals = $1,122.28       $1,229.2758   $1,229.26   $1,229.25   $1,229.30