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 $141.98   11.835%   $158.7833   $158.78   $158.80   $158.80  
  Purchase #2 $218.33   3.269%   $225.4672   $225.47   $225.45   $225.50  
  Purchase #3 $154.98   12.792%   $174.805   $174.81   $174.80   $174.80  
  Purchase #4 $179.40   13.554%   $203.7159   $203.72   $203.70   $203.70  
  Purchase #5 $23.28   11.310%   $25.913   $25.91   $25.90   $25.90  
  Purchase #6 $53.83   12.438%   $60.5254   $60.53   $60.55   $60.50  
  Purchase #7 $198.51   7.176%   $212.7551   $212.76   $212.75   $212.80  
  7 purchase totals = $970.31       $1,061.9649   $1,061.98   $1,061.95   $1,062.00