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 $228.94   13.642%   $260.172   $260.17   $260.15   $260.20  
  Purchase #2 $136.84   13.754%   $155.661   $155.66   $155.65   $155.70  
  Purchase #3 $226.49   8.832%   $246.4936   $246.49   $246.50   $246.50  
  Purchase #4 $65.90   13.232%   $74.6199   $74.62   $74.60   $74.60  
  Purchase #5 $227.45   10.424%   $251.1594   $251.16   $251.15   $251.20  
  Purchase #6 $60.28   4.378%   $62.9191   $62.92   $62.90   $62.90  
  Purchase #7 $241.34   4.175%   $251.4159   $251.42   $251.40   $251.40  
  7 purchase totals = $1,187.24       $1,302.4409   $1,302.44   $1,302.35   $1,302.50